Rotation angle detection device, electric power steering device and method of controlling electric power steering device

ABSTRACT

The power management unit supplies first power that is continuous power to the second sensor when the power switch is on, supplies second power that is intermittent power having a voltage lower than the first power to the second sensor when the power switch is off, and outputs rotation number information representing a rotation number of the motor rotation shaft based on the second sensor signal. The power management unit includes a comparator that operates using the second power as the power source when the power switch is off and compare the second sensor signal and the reference voltage, and a counter that detects the rotation number of the motor rotation shaft by counting the output of the comparators.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a National Stage of International Application No.PCT/JP2021/014712 filed Apr. 7, 2021, claiming priority based onJapanese Patent Application No. 2020-069997 filed Apr. 8, 2020, JapanesePatent Application No. 2020-114168, filed Jul. 1, 2020 and JapanesePatent Application No. 2021-016704 filed Feb. 4, 2021.

TECHNICAL FIELD

The present invention relates to a rotation angle detection device, anelectric power steering device and a method of controlling an electricpower steering device.

BACKGROUND ART

Conventionally, a sensor for detecting a rotation angle of a motorrotation shaft is proposed. In addition, a technology for monitoring arotation number of a rotation shaft of a motor while a power switch isoff is proposed.

For example, the following PTL 1 describes a steering system that ismade redundant by mounting two Magnetic Resistance (MR) sensors thatdetect an angular position of the electric motor and two counting unitsthat process the output signal of the sensors, and counts a rotationnumber of the electric motor by the two counting units based on asine-wave signal and a cosine-wave signal that are output by two MRsensors respectively while the ignition key is off.

CITATION LIST Patent Literature

PTL 1: European Patent No. 2050658

SUMMARY OF INVENTION Technical Problem

For example, in an electric power steering system, while an ignition key(main power switch) is off and an assistance function is stopped, asteering shaft may be rotated due to external force. For this reason, arotation number of a rotation shaft of a motor connected to the steeringshaft is desirable to be monitored by a circuit that is backed up by abattery even while the ignition key is off.

On the other hand, the power consumption while the power switch is offis desirable to be as low as possible. For example, in the case of anelectric power steering system, the main power source is a batterymounted on the vehicle. Therefore, dark current that flows while theignition key is off is required to be as little as possible. Thesteering system described in PTL 1 may lead to an increase in powerconsumption due to the dark current that flows through the sensor whilethe ignition key is off.

The present invention is made in consideration of such a problem, andthe purpose of the present invention is to reduce power consumption of arotation angle detection device including a sensor for outputting asignal in accordance with a rotation of a motor rotation shaft while thepower switch is off.

Solution to Problem

In order to achieve the above-described object, according to an aspectof the present invention, there is provided a rotation angle detectiondevice including: a first sensor that is supplied with power when apower switch is on and outputs a first sensor signal in accordance witha rotation of a motor rotation shaft of a motor, and to which powersupply is stopped when the power switch is off; an angular positioncalculation unit that is supplied with power when the power switch is onand calculates angular position information representing an angularposition of the motor rotation shaft based on the first sensor signal,and to which power supply is stopped when the power switch is off; asecond sensor that outputs a second sensor signal including a sine-wavesignal and a cosine-wave signal in accordance with a rotation of themotor rotation shaft; a power management unit that supplies first powerthat is continuous power to the second sensor when the power switch ison, supplies second power that is intermittent power having a voltagelower than the first power to the second sensor when the power switch isoff, and outputs rotation number information representing a rotationnumber of the motor rotation shaft based on the second sensor signal;and a rotation angle calculation unit that is supplied with power whenthe power switch is on and calculates rotation angle informationrepresenting a rotation angle of the motor rotation shaft based on theangular position information and the rotation number information, and towhich power supply is stopped when the power switch is off.

The power management unit includes: a power supply unit that generatesthe first power and the second power; a comparator that operates usingthe first power supplied from the power supply unit as a power sourceand compares a first reference voltage based on a voltage of the firstpower and the second sensor signal when the power switch is on, andoperates using the second power supplied from the power supply unit as apower source and compares a second reference voltage based on a voltageof the second power and the second sensor signal when the power switchis off; and a counter that detects a rotation number of the motorrotation shaft by counting an output of the comparator.

According to another aspect of the present invention, there is providedan electric power steering device including; a torque sensor configuredto detect steering torque that is applied to a steering shaft based on atorsion angle between an input shaft and an output shaft connected via atorsion bar mounted on a steering shaft of a vehicle; a motor configuredto provide steering assistance force to a steering mechanism of thevehicle; the rotation angle detection device described above configuredto calculate rotation angle information of a motor rotation shaft of themotor; a motor control unit configured to drive and control the motorbased on the steering torque; and a steering angle calculation unitconfigured to calculate a steering angle of the input shaft based on thetorsion angle, a reduction ratio of a reduction gear, and the rotationangle information.

According to another aspect of the present invention, there is provideda control method of the electric power steering device, wherein thesteering assistance force provided by the motor is controlled based onthe steering angle calculated by the steering angle calculation unit.

Advantageous Effects of Invention

According to the present invention, it is possible to reduce powerconsumption of a rotation angle detection device including a sensor foroutputting a signal in accordance with a rotation of a motor rotationshaft while the power switch is off.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a configuration diagram illustrating an outline of anexemplary electric power steering device according to the embodiment.

FIG. 2 is a diagram illustrating an example of a first sine-wave signal,a first cosine-wave signal, a second sine-wave signal, and a secondcosine-wave signal.

FIG. 3 is an exploded diagram illustrating an outline of an exemplarysensor unit.

FIG. 4 is a diagram illustrating a configuration example of acontroller.

FIG. 5 is a block diagram of an exemplary functional configuration of apower management unit of the first embodiment.

FIG. 6A to FIG. 6D are explanatory diagrams of an exemplary operation ofa rotation number detection unit, and FIG. 6E is an explanatory diagramof exemplary rotation number information.

FIG. 7 is a block diagram of an exemplary functional configuration of amicroprocessor.

FIG. 8A is a diagram illustrating a first sine-wave signal SIN 1 and afirst cosine-wave signal COS 1, FIG. 8B is a diagram illustratingexemplary angular position information θ1, FIG. 8C is a diagram of amotor rotation number Nr, and FIG. 8D is a diagram of rotation angleinformation θm.

FIG. 9 is a block diagram of an exemplary functional configuration of anassist control unit.

FIG. 10A is a diagram illustrating a second sine-wave signal SIN 2 and asecond cosine-wave signal COS 2, FIG. 10B is a diagram illustrating anexample of a sine count value CNTs and a cosine count value CNTc whenthere is an error in the threshold voltage Vr of a comparator, and FIG.10C is a diagram of an example of a total count value CNT.

FIG. 11A is an explanatory diagram of an error that may occur in themotor rotation number Nr when a rotation number information correctionunit does not exist, and FIG. 11B is an explanatory diagram of an errorthat may occur in the rotation angle information θm.

FIG. 12 is a block diagram of an exemplary functional configuration ofthe rotation number information correction unit.

FIG. 13A is a diagram illustrating an example of a first quadrant signalQ1 and a second quadrant signal Q2, FIG. 13B is a diagram illustrating adifference of the first quadrant signal Q1 and the second quadrantsignal Q2, FIG. 13C is a diagram illustrating an example of a correctedtotal count value CNTa, and FIG. 13D is a diagram illustrating the motorrotation number Nr calculated from the corrected total count value CNTa.

FIG. 14 is a block diagram of an exemplary functional configuration of apower management unit of the second embodiment.

FIG. 15A to FIG. 15C are explanatory diagrams of an example ofcontrolling a drive interval of a second sensor when a rotation of amotor rotation shaft is detected while an ignition key is off.

FIG. 16A to FIG. 16D are explanatory diagrams of an example ofcontrolling the drive interval of the second sensor when a rotation ofthe motor rotation shaft is not detected while the ignition key is off.

FIG. 17 is a flow chart of an example of a setting method of the driveinterval instructed by a drive interval instruction signal.

FIG. 18 is a flow chart of an exemplary rotation detection process ofFIG. 17 .

FIG. 19A is a diagram illustrating a waveform of an exemplary secondsensor power source Vs2 that is output intermittently while the ignitionkey is off, and FIG. 19B is a diagram illustrating a waveform of asingle intermittent output of the second sensor power source Vs2.

FIG. 20 is a block diagram of an exemplary functional configuration of apower management unit of the third embodiment.

FIG. 21 is a block diagram illustrating an outline of an exemplarycircuit configuration of a sensor unit according to the fourthembodiment.

FIG. 22 is a diagram illustrating a configuration example of acontroller according to the fourth embodiment.

FIG. 23 is a configuration diagram illustrating an outline of an exampleof a modification of electric power steering device.

FIG. 24 is a configuration diagram illustrating an outline of an exampleof a modification of electric power steering device.

FIG. 25 is a configuration diagram illustrating an outline of an exampleof a modification of electric power steering device.

DESCRIPTION OF EMBODIMENTS

Embodiments of the present invention will be described in detail withreference to the drawings. Note that the embodiments of the presentinvention to be described below indicate devices and methods to embodythe technical idea of the present invention by way of example, and thetechnical idea of the present invention does not limit the constitution,arrangements, and the like of the constituent components to thosedescribed below. The technical idea of the present invention can besubjected to a variety of alterations within the technical scopeprescribed by the claims described in CLAIMS.

First Embodiment

Configuration

Hereinafter, a configuration example of a case in which a rotation angledetection device of the embodiment is applied to an Electric PowerSteering (EPS) device that gives rotation force of a motor as thesteering assistance force (assistance force) to a steering mechanism ofa vehicle. The present invention is not limited to a rotation angledetection device applied to an electric power steering but can be widelyapplied to a rotation angle detection device including at least twosensors that output signals in accordance with a rotation of a motorrotation shaft.

Refer to FIG. 1 . Column shafts (steering shafts) 2 i and 2 o of asteering wheel 1 are coupled to a tie rod 6 of steered wheels via areduction gear 3, universal joints 4A and 4B, and a pinion rackmechanism 5. The input shaft 2 i and the output shaft 2 o of the columnshaft are connected by a torsion bar (not illustrated) that twistsaccording to a difference of rotation angles of the input shaft 2 i andthe output shaft 2 o.

A torque sensor 10 electromagnetically measures a torsion angle of thetorsion bar as a steering torque Th of the steering wheel 1.

A motor 20 that assists the steering force of the steering wheel 1 isconnected to the output shaft 2 o of the column shaft via the reductiongear 3.

The controller 40 is an Electronic Control Unit (ECU) that drives andcontrols the motor 20. To the controller 40, battery power Vbat issupplied from a battery 14 that is the power source, and an ignition keysignal IG is input from an ignition key 11 that is a power switch.

The controller 40 calculates a steering assistance command value of theassistance command using an assistance map, etc. based on the steeringtorque Th detected by the torque sensor 10 and vehicle speed Vh detectedby a vehicle speed sensor 12, and supplies driving current I to themotor 20 based on the calculated steering assistance command value.

A sensor unit 30 includes two sensors that each output a sensor signalin accordance with a rotation of the motor rotation shaft of the motor20.

Each of the two sensors in the sensor unit 30 individually detects anangular position θ (θ=0 to 360 deg) of the motor rotation shaft, and oneof the sensors outputs a first sine-wave signal sin 1=A×sin θ+Voff1 anda first cosine-wave signal cos 1=A×cos θ+Voff1 each having an amplitudeof A, and the other sensor outputs a second sine-wave signal sin 2=A×sinθ+Voff2 and a second cosine-wave signal cos 2=A×cos θ+Voff2 each havingan amplitude of A to the controller 40. The voltages Voff1 and Voff2 areoffset voltages (in other words, DC components of the first sine-wavesignal sin 1, the first cosine-wave signal cos 1, the second sine-wavesignal sin 2, and the second cosine-wave signal cos 2). An example ofthe first sine-wave signal sin 1, the first cosine-wave signal cos 1,the second sine-wave signal sin 2 and the second cosine-wave signal cos2 are illustrated in FIG. 2 .

The controller 40 calculates the rotation angle θm of the motor rotationshaft of the motor 20 based on the first sine-wave signal sin 1, thefirst cosine-wave signal cos 1, the second sine-wave signal sin 2, andthe second cosine-wave signal cos 2.

The controller 40 calculates the rotation angle θo of the output shaft 2o of the column shaft based on the rotation angle θm of the motorrotation shaft of the motor 20 and the gear ratio Rg of the reductiongear 3. The controller 40 calculates the rotation angle θi of the inputshaft 2 i of the column shaft, in other words, the steering angle θs ofthe steering wheel 1, based on the rotation angle θo and the steeringtorque Th.

In the electric power steering device having the above-mentionedconfiguration, the steering torque Th that is caused by a driveroperating the steering handle and transmitted from the steering wheel 1is detected by the torque sensor 10, and the motor 20 is driven andcontrolled by the steering assistance command value calculated based onthe steering torque Th and the vehicle speed Vh, and the assistanceforce (steering assistance force) for the steering wheel operation bythe driver is provided to the steering system.

FIG. 3 is an exploded diagram illustrating an outline of the exemplarysensor unit 30. The sensor unit 30 includes a magnet 31 and a circuitsubstrate 32.

The magnet 31 is fixed to an end 24 that is the opposite of the outputend 22 of the motor rotation shaft 21 of the motor 20 and has differentpoles (south pole and north pole) that are arranged along thecircumferential direction of the motor rotation shaft 21.

A first sensor 33 and a second sensor 34 that output a first sensorsignal and a second sensor signal respectively in accordance with therotation of the motor rotation shaft 21 of the motor 20 by detecting themagnetic flux generated by the magnet 31 are mounted on the circuitsubstrate 32.

The first sensor signal that is output from the first sensor 33 includesa first sine-wave signal sin 1 and a first cosine-wave signal cos 1. Thesecond sensor signal that is output from the second sensor 34 includes asecond sine-wave signal sin 2 and a second cosine-wave signal cos 2.

The first sensor 33 and the second sensor 34 may be MR sensors (forexample, Tunnel Magneto Resistance (TMR) sensors) that detect magneticflux, for example.

The first sensor 33 and the second sensor 34 are arranged near themagnet 31 that rotates with the motor rotation shaft 21, andrespectively generate the first sine-wave signal sin 1 and the firstcosine-wave signal cos 1 and the second sine-wave signal sin 2 and thesecond cosine-wave signal cos 2 in accordance with the rotation of themotor rotation shaft 21 by detecting the magnetic flux generated by themagnet 31.

The sensor unit 30 is formed as a unit separate from the controller 40,and connected to the controller 40 by a harness 35. The controller 40supplies the first sensor power source Vs1 and a second sensor powersource Vs2 that respectively drive the first sensor 33 and the secondsensor 34 to the sensor unit 30 via the harness 35. The sensor unit 30outputs the first sensor signal and the second sensor signal to thecontroller 40 via the harness 35. The length of the harness 35 may be 10cm, for example.

The sensor unit 30 and the controller 40 may be formed as a single unit.In this case, the first sensor 33 and the second sensor 34 may be builtdirectly into the controller 40, and the controller 40 may be attachedto an end opposite from the output end 22 of the motor 20.

The configuration of the sensor unit 30 is not limited to theconfiguration illustrated in FIG. 3 . The first sensor 33 and the secondsensor 34 of the sensor unit 30 may be a sensor of a type other than MRsensor. The first sensor 33 may be any sensor that outputs a signal inaccordance with a rotation of the motor rotation shaft 21. The secondsensor 34 may be any sensor that outputs a sine-wave signal and acosine-wave signal in accordance with a rotation of the motor rotationshaft 21.

With reference to FIG. 4 , a configuration example of the controller 40is explained. The controller 40 includes a power management unit 50 anda Micro-Processing Unit (MPU) 60.

The power management unit 50 is supplied with battery power Vbat fromthe battery 14, and manage the power of the sensor unit 30 and thecontroller 40. The power management unit 50 may be implemented as asingle Integrated Circuit (IC) chip. The power management unit 50 may bea power management Integrated Circuit (IC), for example.

The power management unit 50 generates the first sensor power source Vs1for driving the first sensor 33, the second sensor power source Vs2 fordriving the second sensor 34, a power source Vm for driving the MPU60,the controller 40 and other components (hereinafter may be referred toas MPU60, etc.) from the power supplied from the battery 14, based onthe ignition key signal IG.

The voltage of the first sensor power source Vs1, the second sensorpower source Vs2, and the power source Vm may be a common power voltageVcc1 (not illustrated), for example. The power voltage Vcc1 may be 5 V,for example.

The power management unit 50 supplies the first sensor power source Vs1,the second sensor power source Vs2, and the power source Vm, to thefirst sensor 33, the second sensor 34, and the MPU 60, etc.,respectively while the ignition key 11 is on.

On the other hand, the power management unit 50 stops providing thefirst sensor power source Vs1 and the power source Vm to the firstsensor 33 and the MPU 60, etc. while the ignition key 11 is off. Thepower management unit 50 supplies the second sensor power source Vs2 tothe second sensor 34 intermittently at a predetermined cycle T. Thevoltage of the second sensor power source Vs2 that is supplied while theignition key 11 is off may be lower than the voltage Vcc1 while theignition key 11 is on.

The power management unit 50 generates rotation number informationrepresenting a rotation number by detecting the rotation number of themotor rotation shaft 21 based on the second sine-wave signal sin 2 andthe second cosine-wave signal cos 2. The rotation number informationincludes the sine count value CNTs counting the change of the sign ofthe second sine-wave signal sin 2, and the cosine count value CNTccounting the change of the sign of the second cosine-wave signal cos 2.The sine count value CNTs and the cosine count value CNTc changeaccording to the combination of the sign of the second sine-wave signalsin 2 and the sign of the second cosine-wave signal cos 2. The detailsof the power management unit 50 will be described later.

The MPU 60 calculates the steering assistance command value of theassistance command using an assistance map, etc. based on the steeringtorque Th detected by the torque sensor 10 and the vehicle speed Vhdetected by a vehicle speed sensor 12 and controls the driving current Iof the motor 20.

The MPU 60 calculates angular position information θ1 representing anangular position of the motor rotation shaft 21 based on the firstsine-wave signal sin 1 and the first cosine-wave signal cost. Theangular position information θ1 represents the angular position withinthe angular range of one rotation of the motor rotation shaft 21 (θ1=0to 360 deg).

The MPU 60 calculates rotation angle information θm representing arotation angle of the motor rotation shaft 21 based on the rotationnumber information (the sine count value CNTs and the cosine count valueCNTc) generated by the power management unit 50 and the angular positioninformation θ1. The rotation angle information θm represents therotation angle within the angular range of multiple turns that is morethan one rotation of the motor rotation shaft 21.

More specifically, since the power source Vm is not supplied to the MPU60 while the ignition key 11 is off, the MPU 60 stops operation.

When the ignition key 11 is turned on from off, the MPU 60 reads therotation number information from the power management unit 50 andcalculates the rotation angle information θm based on the rotationnumber information and the angular position information θ1.

While the ignition key 11 is on, the MPU 60 accumulates the change ofthe angle of the angular position information θ1 after the time at whichthe ignition key 11 is turned on from off to the rotation angleinformation θm calculated when the ignition key 11 is turned on fromoff, and calculates the rotation angle information θm after the ignitionkey 11 is turned on from off.

The MPU 60 calculates the rotation angle θo of the output shaft 2 o ofthe column shaft by multiplying the rotation angle information θm by thegear ratio Rg of the reduction gear 3. Based on the steering torque Thdetected by the torque sensor 10, the torsion angle θt of the torsionbar arranged at the column shaft is calculated, and the rotation angleθi of the input shaft 2 i of the column shaft (steering angle θs of thesteering wheel 1) is calculated by adding the torsion angle θt to therotation angle θo of the output shaft 2 o.

The controller 40 may control the steering assistance force that isapplied to the output shaft 2 o by the motor 20 based on the rotationangle information of the rotation angle θo of the output shaft 2 o andthe rotation angle θi of the input shaft 2 i. For example, thecontroller 40 may determine whether the column shaft is in a state inwhich the steering wheel is steered to the end or not based on therotation angle information. When the column shaft is in a state in whichthe steering wheel is steered to the end, the controller 40 may limitthe driving current I of the motor 20 and may correct to reduce thesteering assistance force. The controller 40 may use the rotation angleinformation of the rotation angle θi of the input shaft 2 i for thedetermination of whether the input shaft 2 i is in a neutral position.

Also, for example, the controller 40 may determine whether the driverfurther turns the steering wheel 1 or the driver returns the steeringwheel 1 based on the rotation angle information. For example, thecontroller 40 may determine whether the driver further turns thesteering wheel or the driver returns the steering wheel based on therotation angle of the column shaft and its changing direction. Thecontroller 40 may determine whether the driver further turns thesteering wheel or the driver returns the steering wheel based on therotation angle of the column shaft and the steering torque Th.

The controller 40 may increase and correct the driving current I toincrease the steering assistance force when the driver further turns thesteering wheel, and decrease and correct the driving current I todecrease the steering assistance force when the driver returns thesteering wheel. More details of the MPU 60 will be described later.

With reference to FIG. 5 , a functional configuration example of a powermanagement unit 50 is explained. The power management unit 50 includes aregulator 51, a first power supply unit 52, a second power supply unit53, a third power supply unit 54, a power control unit 56, and arotation number detection unit 58.

The regulator 51, the first power supply unit 52, the second powersupply unit 53, the third power supply unit 54 and the power controlunit 56 are an example of a “power supply unit” described in the claims.

The regulator 51 generates regulator power source VR having apredetermined voltage from the battery power source Vbat. The voltage ofthe regulator power source VR is 6 V, for example. The first powersupply unit 52, the second power supply unit 53, and the third powersupply unit 54 generate the power source Vm, the first sensor powersource Vs1, and the second sensor power source Vs2, respectively fromthe regulator power source VR.

The power source Vm and the first sensor power source Vs1 may be madecommon, and the first power supply unit 52 and the second power supplyunit 53 may become a single power supply unit. In other words, the firstsensor 33 and the MPU 60, etc. may be supplied with power from one or aplurality of power supply units.

The power control unit 56 outputs control signals Sc1, Sc2, and Sc3 tothe first power supply unit 52, the second power supply unit 53 and thethird power supply unit 54, respectively, based on the ignition keysignal IG and controls the first power supply unit 52, the second powersupply unit 53, and the third power supply unit 54.

While the ignition key 11 is on, the power control unit 56 makes thefirst power supply unit 52, the second power supply unit 53, and thethird power supply unit 54 generate the power source Vm, the firstsensor power source Vs1, and the second sensor power source Vs2,respectively. The first power supply unit 52 continually supplies powersource Vm to the MPU 60, etc. The second power supply unit 53continually supplies the first sensor power source Vs1 to the firstsensor 33. The third power supply unit 54 continually supplies thesecond sensor power source Vs2 to the second sensor 34 and the rotationnumber detection unit 58. Therefore, the MPU 60, etc., the first sensor33, the second sensor 34, and the rotation number detection unit 58operate continually.

While the ignition key 11 is off, the power control unit 56 stops thefirst power supply unit 52 and the second power supply unit 53. In otherwords, the generation of the power source Vm and the first sensor powersource Vs1 is stopped. Accordingly, the supply of the first sensor powersource Vs1 to the first sensor 33 and the supply of the power source Vmto the MPU 60, etc. are stopped, and the operation of the first sensor33 and the MPU 60, etc. stop.

On the other hand, the power control unit 56 makes the third powersupply unit 54 generate the second sensor power source Vs2intermittently in a predetermined cycle T. Therefore, the second sensorpower source Vs2 is intermittently supplied to the second sensor 34 andthe rotation number detection unit 58. The second sensor 34 and therotation number detection unit 58 operate intermittently in apredetermined cycle T. The power control unit 56 may set the voltage ofthe second sensor power source Vs2 that is supplied while the ignitionkey 11 is off to be lower than the while the ignition key 11 is on.

The rotation number detection unit 58 generates rotation numberinformation (in other words, the sine count value CNTs and the cosinecount value CNTc) representing a rotation number by detecting therotation number of the motor rotation shaft 21 based on the secondsine-wave signal sin 2 and the second cosine-wave signal cos 2.

The rotation number detection unit 58 includes a first comparator 58 a,a second comparator 58 b, sine counter 58 c, and a cosine counter 58 d.

The first comparator 58 a generates a sign signal Cs representing theplus/minus sign of the second sine-wave signal sin 2 by comparing thesecond sine-wave signal sin 2 and the threshold voltage Vr. The signsignal Cs has a value of “1” when the second sine-wave signal sin 2 isequal to or greater than the threshold voltage Vr and has a value of “0”when the second sine-wave signal sin 2 is less than the thresholdvoltage Vr.

The second comparator 58 b generates a sign signal Cc representing theplus/minus sign of the second cosine-wave signal cos 2 by comparing thesecond cosine-wave signal cos 2 and the threshold voltage Vr. The signsignal Cc has a value of “1” when the second cosine-wave signal cos 2 isequal to or greater than the threshold voltage Vr, and has a value of“0” when the second cosine-wave signal cos 2 is less than the thresholdvoltage Vr.

Since the second sine-wave signal sin 2 and the second cosine-wavesignal cos 2 have a DC offset element Voff2, the threshold voltage Vrmay be set to the offset voltage Voff2, for example.

These sign signals Cs and Cc are input to the sine counter 58 c and thecosine counter 58 d.

Refer to FIG. 6A and FIG. 6B. The waveform in the broken line in FIG. 6Arepresents the second sine-wave signal sin 2, and the waveform in thesolid line represents the second cosine-wave signal cos 2.

The amplitude A of the second sine-wave signal sin 2 and the secondcosine-wave signal cos 2 of the embodiment is one-half of the voltage ofthe second sensor power source Vs2 (in other words, Vs2/2), and the DCcomponent is offset by one-half of the voltage of the second sensorpower source Vs2, and the second sine-wave signal sin 2 and the secondcosine-wave signal cos 2 change in the range of 0 V to the voltage ofthe second sensor power source Vs2 (in other words, Vs2). Therefore, thethreshold voltage Vr is set to one-half of the second sensor powersource Vs2 (in other words, Vs2/2).

The sign signal Cs of the second sine-wave signal sin 2 output from thefirst comparator 58 a has a value of “1” when the angular position ofthe motor rotation shaft 21 is in the range of 0 deg to 180 deg and hasa value of “0” in the range of 180 deg to 360 deg.

The sign signal Cc of the second cosine-wave signal cos 2 output fromthe second comparator 58 b has a value of “1” when the angular positionof the motor rotation shaft 21 is in the range of 0 deg to 90 deg and270 deg to 360 deg and has a value of “0” in the range of 90 deg to 270deg.

Refer to FIG. 5 . The sine counter 58 c and the cosine counter 58 dcount the change of the combination of the signs of the second sine-wavesignal sin 2 and the second cosine-wave signal cos 2 based on the signsignal Cs of the second sine-wave signal sin 2 and the sign signal Cc ofthe second cosine-wave signal cos 2, and calculates the sine count valueCNTs and the cosine count value CNTc, respectively.

Refer to FIG. 6C and FIG. 6D. The sine counter 58 c calculates the sinecount value CNTs by counting the number of changes of the sign of thesecond sine-wave signal sin 2, and the cosine counter 58 d calculatesthe cosine count value CNTc by counting the number of changes of thesign of the second cosine-wave signal cos 2. The sine counter 58 c andthe cosine counter 58 d store the calculated sine count value CNTs andthe cosine count value CNTc in a non-volatile memory (not illustrated),for example.

More specifically, the sine counter 58 c increases the sine count valueCNTs by 1 when the value of the sign signal Cs of the second sine-wavesignal sin 2 changes from “0” to “1” while the sign signal Cc of thesecond cosine-wave signal cos 2 has a value of “1”, and decreases thesine count value CNTs by 1 when the value of the sign signal Cs of thesecond sine-wave signal sin 2 changes from “1” to “0”.

The sine counter 58 c increases the sine count value CNTs by 1 when thevalue of the sign signal Cs of the second sine-wave signal sin 2 changesfrom “1” to “0” while the sign signal Cc of the second cosine-wavesignal cos 2 has a value of 0, and decreases the sine count value CNTsby 1 when the value of the sign signal Cs of the second sine-wave signalsin 2 changes from “0” to “1”.

The cosine counter 58 d increases the cosine count value CNTc by 1 whenthe value of the sign signal Cc of the second cosine-wave signal cos 2changes from “0” to “1” while the sign signal Cs of the second sine-wavesignal sin 2 has a value of “0”, and decreases the cosine count valueCNTc by 1 when the value of the sign signal Cc of the second cosine-wavesignal cos 2 changes from “1” to “0”.

The cosine counter 58 d increases the cosine count value CNTc by 1 whenthe value of the sign signal Cc of the second cosine-wave signal cos 2changes from “1” to “0” while the sign signal Cs of the second sine-wavesignal sin 2 has a value of “1”, and decreases the cosine count valueCNTc by 1 when the value of the sign signal Cc of the second cosine-wavesignal cos 2 changes from “0” to “1”.

As a result, when the motor rotation shaft 21 makes one rotation, thesine count value CNTs and the cosine count value CNTc increase ordecrease by 2, depending on the rotation direction. Therefore, when themotor rotation shaft 21 makes one rotation, the sum of the sine countvalue CNTs and the cosine count value CNTc (hereinafter may be expressedas “total count value CNT”) increases or decreases by 4, depending onthe rotation direction, as illustrated in FIG. 6E. Accordingly, thecombination of the sine count value CNTs and the cosine count value CNTcand the total count value CNT represent the rotation number in quartersof a rotation. The combination of sine count value CNTs and the cosinecount value CNTc and the total count value CNT represent which of the 4quadrants made by dividing into four the rotation range of the motorrotation shaft 21 the angular position of the motor rotation shaft 21belongs to.

The sine count value CNTs and the cosine count value CNTc of theembodiment are merely an example, and the rotation number information ofthe present invention is not limited to the sine count value CNTs andthe cosine count value CNTc. The rotation number information may be anyrotation number information representing the rotation number in units of1/n rotations where n is a natural number of 2 and more.

With reference to FIG. 7 , a functional configuration example of the MPU60 is explained. The MPU 60 includes an angular position calculationunit 61, a count total unit 62, a rotation number information correctionunit 63, a rotation number calculation unit 64, a torsion anglecalculation unit 65, a rotation angle information calculation unit 66, adiagnosis unit 67, and an assist control unit 68.

The functions of the angular position calculation unit 61, the counttotal unit 62, the rotation number information correction unit 63, therotation number calculation unit 64, the torsion angle calculation unit65, the rotation angle information calculation unit 66, the diagnosisunit 67, and the assist control unit 68 are realized by MPU 60 executinga program stored in a storage device (a non-volatile memory, etc. forexample) included by the MPU 60 or the controller 40.

The rotation angle information calculation unit 66 is an example of the“rotation angle calculation unit” and the “steering angle calculationunit” described in the claims. The assist control unit 68 is an exampleof the “motor control unit” described in the claims.

the angular position calculation unit 61 takes the first sine-wavesignal sin 1 and the first cosine-wave signal cos 1 as inputs, andcompensates the error included in these signals (offset, amplitudedifference, phase difference, etc.). FIG. 8A illustrates an example ofthe first sine-wave signal sin 1 and the first cosine-wave signal cos 1.The angular position calculation unit 61 calculates the angular positioninformation θ1 representing an angular position of the motor rotationshaft 21 within the range of 1 rotation (θ1=0 to 360 deg) based on thefirst sine-wave signal sin 1 and the first cosine-wave signal cos 1after the error is compensated. An example of the angular positioninformation el is illustrated in FIG. 8B.

For example, the angular position calculation unit 61 may calculate theangular position information θ1 based on the sum of the first sine-wavesignal sin 1 and the first cosine-wave signal cos 1 (cos 1+sin 1) andthe difference (cos 1−sin 1).

Similarly, the angular position calculation unit 61 takes the secondsine-wave signal sin 2 and the second cosine-wave signal cos 2 asinputs, compensates the error included therein, and calculates theangular position information θ2 representing an angular position of themotor rotation shaft 21 within the range of 1 rotation (θ2=0 to 360deg).

Refer to FIG. 7 . The count total unit 62 reads the sine count valueCNTs and the cosine count value CNTc respectively from the sine counter58 c and the cosine counter 58 d of the power management unit 50 whenthe supply of the power source Vm to the MPU 60 starts (in other words,when the ignition key 11 is turned on from off). The count total unit 62adds the sine count value CNTs and the cosine count value CNTc andcalculates the total count value CNT as illustrated in FIG. 6E.

Here, an error may occur to the sine count value CNTs and the cosinecount value CNTc due to an error included in the second sine-wave signalsin 2 and the second cosine-wave signal cos 2 and an error in thethreshold voltage of the comparator Vr. As a result, the total countvalue CNT may include an error.

Refer to FIG. 7 . The rotation number information correction unit 63compensates for the error generated in the total count value CNT bycorrecting the total count value CNT based on the angular positioninformation θ1. The rotation number information correction unit 63outputs the corrected total count value CNTa in which the error iscompensated. The details of the rotation number information correctionunit 63 will be described later.

The rotation number calculation unit 64 calculates the rotation numberNr of the motor rotation shaft 21 as the quotient obtained by dividingthe corrected total count value CNTa by a natural number n. The naturalnumber n is the number of increases/decreases of the total count valueCNT per one rotation of the motor rotation shaft 21, and the naturalnumber n is 4 in this embodiment. An example of the rotation number Nris illustrated in FIG. 8C.

The torsion angle calculation unit 65 calculates the torsion angle θt ofthe torsion bar arranged on the column shaft based on the steeringtorque Th detected by the torque sensor 10.

Refer to FIG. 7 . The rotation angle information calculation unit 66calculates the rotation angle information θm in the range of multiplerotations of equal to or more than one rotation of the motor rotationshaft 21 based on the rotation number Nr calculated by the rotationnumber calculation unit 64 and the angular position information θ1calculated by the angular position calculation unit 61 when the supplyof the power source Vm to the MPU 60 is started (in other words, theignition key 11 is turned on from off).

The rotation angle information calculation unit 66 calculates therotation angle information θm=(360 deg×rotation number Nr)+angularposition information θ1 by means of a multiplier 66 a and an adder 66 b.An example of the rotation angle information θm is illustrated in FIG.8D.

Afterwards, while the ignition key 11 is on, the rotation angleinformation calculation unit 66 accumulates the change of the angle ofthe angular position information θ1 after the time at which the ignitionkey 11 is turned on from off to the rotation angle information θmcalculated when the ignition key 11 is turned on from off, andcalculates the rotation angle information θm after the ignition key 11is turned on from off.

Refer to FIG. 7 . The multiplier 66 c calculates the rotation angle θoof the output shaft 2 o of the column shaft by multiplying the rotationangle information θm by the gear ratio Rg of the reduction gear 3. Theadder 66 d calculates the rotation angle θi (the steering angle θs ofthe steering wheel 1) of the input shaft 2 i of the column shaft byadding the torsion angle θt of the torsion bar to the rotation angle θo.The rotation angle information calculation unit 66 outputs the rotationangle information including the rotation angle θo and the rotation angleθi.

The rotation angle information including the rotation angle θo of theoutput shaft 2 o and the rotation angle θi of the input shaft 2 i can beused for the determination by the controller 40 whether the column shaftis steered to an end or not and the determination whether the driverfurther turns the steering wheel 1 or returns the steering wheel. Thecontroller 40 may control the steering assistance force that is appliedto the output shaft 2 o by the motor 20 based on these determinationresults. The rotation angle information of the rotation angle θi of theinput shaft 2 i may be used for the determination of whether the inputshaft 2 i is in a neutral position.

The diagnosis unit 67 determines the abnormality that occurred in thefirst sensor 33 or the second sensor 34 by comparing the angularposition information θ1 calculated based on the first sine-wave signalsin 1 and the first cosine-wave signal cos 1 and the angular positioninformation θ2 calculated based on the second sine-wave signal sin 2 andthe second cosine-wave signal cos 2. For example, when the differencebetween the angular position information θ1 and the angular positioninformation θ2 is equal to or greater than a threshold value, thediagnosis unit 67 determines that an abnormality has occurred in thefirst sensor 33 or the second sensor 34.

The diagnosis unit 67 determines an abnormality that occurred in thesecond sensor 34 or the rotation number detection unit 58 based on thedifference between the sine count value CNTs and the cosine count valueCNTc. For example, the diagnosis unit 67 determines an abnormality hasoccurred in the second sensor 34 or the rotation number detection unit58 when the difference between the sine count value CNTs and the cosinecount value CNTc is equal to or greater than 2.

The diagnosis unit 67 outputs a diagnosis signal Sd representing thedetermination result to the assist control unit 68.

The assist control unit 68 controls the driving current I of the motor20 based on the steering torque Th detected by the torque sensor 10 andthe vehicle speed Vh detected by the vehicle speed sensor 12.

FIG. 9 illustrates an exemplary functional configuration of the assistcontrol unit 68. The steering torque Th detected by the torque sensor 10and the vehicle speed Vh detected by the vehicle speed sensor 12 areinput to a current command value calculation unit 71 that calculates thecurrent command value Iref1. The current command value calculation unit71 calculates the current command value Iref1 that is the target valueof the current to be supplied to the motor 20 based on the inputsteering torque Th and the vehicle speed Vh using an assistance map,etc.

The current command value Iref1 is input to a current limit unit 73 viaan addition unit 72A, and the current command value Irefm whose maximumcurrent is limited is input to the subtraction unit 72B, the deviationΔI (=Irefm−Im) from the motor current value Im being fed back iscalculated, and the deviation ΔI is input to the PI(proportional-integral) control unit 75 for improving the characteristicof the steering operation. The voltage control command value Vref whosecharacteristic is improved by the PI control unit 75 is input to the PWMcontrol unit 76, and the motor 20 is PWM driven via an inverter 77 asthe driver. The current value Im of the motor 20 is detected by themotor current detector 78 and fed back to the subtraction unit 72B.

A compensation signal CM from a compensation signal generation unit 74is added to the addition unit 72A, and the characteristics of thesteering system are compensated by adding the compensation signal CM,thereby improving astringency and inertial characteristics, etc. Thecompensation signal generation unit 74 adds the self-aligning torque(SAT) 74-3 and the inertia 74-2 at the addition unit 74-4, and furtheradds the astringency 74-1 at the addition unit 74-5, and the result ofthe addition by the addition unit 74-5 is the compensation signal CM.

Refer to FIG. 7 . The assist control unit 68 performs a predeterminedabnormality handling processing such as stopping driving the motor 20and outputting alarm when an occurrence of abnormality is detected basedon the diagnosis signal Sd output by the diagnosis unit 67.

The rotation number information correction unit 63 is described. Asdescribed above, an error may occur to the total count value CNTs outputfrom the rotation number calculation unit 64 due to the error includedin the second sine-wave signal sin 2 and the second cosine-wave signalcos 2 and the error in the threshold voltage of the comparator Vr.

Hereinafter, the error that occurs to the total count value CNT byexemplifying a case that the threshold voltage of the comparator Vrcontains an error.

FIG. 10A illustrates an example of the second sine-wave signal sin 2 andthe second cosine-wave signal cos 2, and the threshold voltage Vr of thefirst comparator 58 a and the second comparator 58 b. The broken linerepresents the second sine-wave signal sin 2, the solid line representsthe second cosine-wave signal cos 2, the two-dot chain line representsthe threshold voltage Vr that is compared with the second sine-wavesignal sin 2 at the first comparator 58 a, and the dashed linerepresents the threshold voltage Vr that is compared with the secondcosine-wave signal cos 2 at the second comparator 58 b.

In this example, the threshold voltage Vr (two-dot chain line) that iscompared with the second sine-wave signal sin 2 is lower than the designvalue (ideal value).

As a result, the sine count value CNTs and the cosine count value CNTcwill be as illustrated in FIG. 10B. The broken line represents the sinecount value CNTs, and the solid line represents the cosine count valueCNTc.

As illustrated, there is a gap in the rise (fall) timing of the sinecount value CNTs that should occur when the motor rotation angle is 180,360, 540, 720, 900, 1080 . . . deg.

As a result, there is a gap in the rise (fall) timing of the total countvalue CNT, as illustrated in FIG. 10C. As illustrated with the enclosingdashed line, there is a gap in the rise (fall) timing of the total countvalue CNT that should occur when the motor rotation angle is 180, 360,540, 720, 900, 1080 . . . deg.

As described above, errors occur to the total count value CNT as thetiming in the rise (fall) timing of the total count value CNT due to theerrors included in the second sine-wave signal sin 2 and the secondcosine-wave signal cos 2 and the error in the threshold voltage of thecomparator Vr.

When the rise (fall) timing of the total count value CNT shifts, asillustrated in FIG. 11A, the rise (fall) timing of the motor rotationnumber Nr calculated by the rotation number calculation unit 64 shiftsfrom the original timing.

When the rotation angle information θm is calculated using this motorrotation number Nr, as illustrated in FIG. 11B, the rotation number willbe wrong in the places enclosed by the dashed line, thereby generatingan error in the rotation angle information θm.

The rotation number information correction unit 63 corrects the gap inthe rise (fall) timing of the total count value CNT illustrated in FIG.10C.

Refer to FIG. 12 . The rotation number information correction 63includes a first quadrant information calculation unit 63 a, a secondquadrant information calculation unit 63 b, a quadrant comparison unit63 c, and a correction unit 63 d.

The first quadrant information calculation unit 63 a calculates firstquadrant information Q1 representing which of the quadrants formed bydividing the rotation range of the motor rotation shaft 21 by theabove-described natural number n the angular position of the motorrotation shaft 21 belongs to based on the angular position informationel.

The second quadrant information calculation unit 63 b calculates secondquadrant information Q2 representing which of the quadrants formed bydividing the rotation range of the motor rotation shaft by theabove-described natural number n the angular position of the motorrotation shaft 21 belongs to based on the total count value CNT that isthe rotation number information.

As described above, the natural number n is the number ofincreases/decreases of the total count value CNT per one rotation of themotor rotation shaft 21, and in the embodiment, the natural number n is“4”. The first quadrant information Q1 and the second quadrantinformation Q2 represent which of the first quadrant, the secondquadrant, the third quadrant, and the fourth quadrant the angularposition of the motor rotation shaft 21 belongs to.

The first quadrant information calculation unit 63 a may calculate thefirst quadrant information Q1 by performing a threshold determination ofwhich of the first quadrant to the nth quadrant the angular positioninformation el belongs to.

The second quadrant information calculation unit 63 b may calculate thesecond quadrant information Q2 as the remainder (modulo: CNT mod n) whenthe total count value CNT is divided by the natural number n.

FIG. 13A illustrates an example of the first quadrant information Q1 andthe second quadrant information Q2. The solid line illustrates the firstquadrant information Q1 and the broken line illustrates the secondquadrant information Q2. Due to the gap of the rise (fall) timing of thetotal count value CNT illustrated in FIG. 10C, a difference is generatedbetween the first quadrant information Q1 and the second quadrantinformation Q2 in the places enclosed by the dashed line.

Refer to FIG. 12 . The quadrant comparison unit 63 c outputs a quadrantdifference representing a comparison result of comparing the firstquadrant information Q1 and the second quadrant information Q2.

For example, the quadrant comparison unit 63 c may calculate thedifference by subtracting the number indicating the quadrant of thesecond quadrant information Q2 from the number indicating the quadrantof the first quadrant information Q1 as the quadrant difference inaccordance with the following equation (1).Quadrant difference=Q2−Q1  (1)

However, when the second quadrant information Q2 represents the firstquadrant and the first quadrant information Q1 represents the fourthquadrant, the quadrant difference is calculated by adding 4 (i.e., thenatural number n) to the subtraction result, in accordance with thefollowing equation (2).Quadrant difference=Q2−Q1+4, where Q1=the fourth quadrant, Q2=the firstquadrant  (2)

When the second quadrant information Q2 represents the fourth quadrantand the first quadrant information Q1 represents the first quadrant, thequadrant difference is calculated by subtracting 4 (i.e., the naturalnumber n) from the subtraction result, in accordance with the followingequation (3).Quadrant difference=Q2−Q1−4, where Q1=the first quadrant, Q2=the fourthquadrant  (3)

FIG. 13B represents an example of the quadrant difference. In accordancewith the first quadrant information Q1 and the second quadrantinformation Q2 in FIG. 13A, the quadrant difference takes one of thevalues 1, 0, and −1.

Refer to FIG. 12 . The correction unit 63 d calculates the correctedtotal count value CNTa by correcting the total count value CNT inaccordance with the quadrant difference output by the quadrantcomparison unit 63 c.

For example, the correction unit 63 d calculates the corrected totalcount value CNTa by subtracting the quadrant difference from the totalcount value CNT.

FIG. 13C illustrates the corrected total count value CNTa calculated bysubtracting the quadrant difference of FIG. 13B from the total countvalue CNT of FIG. 10C.

Comparing FIG. 10C and FIG. 13C, the gap in the rise (fall) timing whenthe motor rotation angle is 180, 360, 540, 720, 900, 1080 . . . deg iscorrected.

FIG. 13D is obtained by calculating the motor rotation number Nr basedon the corrected total count value CNTa. The motor rotation number Nr inFIG. 13D is similar to the motor rotation number Nr of FIG. 8C,indicating that the error is corrected.

Operation

The operation of the motor control device of the embodiment isdescribed.

(1) The Period when the Ignition Key is Off

The power control unit 56 of the power management unit 50 stops thefirst power supply unit 52 and the second power supply unit 53, and onlythe third power supply unit 54 operates. At this time, the power controlunit 56 makes the third power supply unit 54 generate the second sensorpower source Vs2 intermittently in a predetermined cycle T.

The second sensor power source Vs2 is intermittently supplied to thesecond sensor 34 and the rotation number detection unit 58. The secondsensor 34 and the rotation number detection unit 58 operateintermittently in a predetermined cycle T.

In the period when the rotation number detection unit 58 operates, thesine counter 58 c increments or decrements the sine count value CNTs inaccordance with the output of the first comparator 58 a. The cosinecounter 58 d increments or decrements the cosine count value CNTc inaccordance with the output of the second comparator 58 b.

As described above, in the period when the ignition key 11 is off, onlythe power management unit 50 and the second sensor 34 continueoperation, and other MPU 60, etc. and the first sensor 33 stopoperation.

(2) The Point when the Ignition Key is Turned on from Off

The power control unit 56 starts operation of the first power supplyunit 52 and the second power supply unit 53. The power control unit 56makes the first power supply unit 52, the second power supply unit 53,and the third power supply unit 54 continually generate the power sourceVm, the first sensor power source Vs1, and the second sensor powersource Vs2. The power source Vm, the first sensor power source Vs1, thesecond sensor power source Vs2 are started to be continually supplied tothe MPU 60, etc., the first sensor 33, the second sensor 34, and therotation number detection unit 58. As a result, in the period when theignition key 11 is on, the MPU 60, etc., the first sensor 33, the secondsensor 34, and the rotation number detection unit 58 operatecontinually.

The count total unit 62 of the MPU 60 reads the sine count value CNTsand the cosine count value CNTc respectively from the sine counter 58 cand the cosine counter 58 d and calculates the total count value CNTwhen the ignition key 11 is turned on from off.

The rotation number information correction unit 63 outputs the correctedtotal count value CNTa by correcting the total count value CNT, and therotation number calculation unit 64 calculates the rotation number Nr ofthe motor rotation shaft 21 from the corrected total count value CNTa.

The angular position calculation unit 61 calculates the angular positioninformation θ1 and based on the rotation number Nr and angular positioninformation θ1, the rotation angle information calculation unit 66calculates the rotation angle information θm of the motor rotation shaft21.

(3) The Period when the Ignition Key is Off

The power control unit 56 operates the first power supply unit 52, thesecond power supply unit 53, and the third power supply unit 54 andmakes them continually generate the power source Vm, the first sensorpower source Vs1, and the second sensor power source Vs2. The MPU 60,etc., the first sensor 33, the second sensor 34, and the rotation numberdetection unit 58 operate continually.

The rotation number detection unit 58 periodically measures the outputof the first comparator 58 a and the second comparator 58 b andmaintains the sine count value CNTs and the cosine count value CNTc (inother words, the current value of the motor rotation number) byincrementing or decrementing the sine count value CNTs and the cosinecount value CNTc.

The angular position calculation unit 61 calculates the angular positioninformation θ1. The rotation angle information calculation unit 66accumulates the change of the angle of the angular position informationθ1 after the time at which the ignition key 11 is turned on from off tothe rotation angle information θm calculated when the ignition key 11 isturned on from off and calculates the rotation angle information θmafter the ignition key 11 is turned on from off.

The rotation angle information calculation unit 66 calculates therotation angle θo of the output shaft 2 o of the column shaft and therotation angle θi of the input shaft 2 i based on the rotation angleinformation θm, the gear ratio Rg of the reduction gear 3, and thetorsion angle θt of the torsion bar.

The assist control unit 68 controls the driving current I of the motor20 based on the steering torque Th detected by the torque sensor 10 andthe vehicle speed Vh detected by the vehicle speed sensor 12.

The diagnosis unit 67 determines whether or not an abnormality hasoccurred in the first sensor 33 or the second sensor 34 by comparing theangular position information θ1 and the angular position information θ2.

The diagnosis unit 67 determines whether or not an abnormality thatoccurred in the second sensor 34 or the rotation number detection unit58 based on the difference between the sine count value CNTs and thecosine count value CNTc.

The assist control unit 68 performs a predetermined abnormality handlingprocessing such as stopping driving the motor 20 and outputting an alarmwhen an occurrence of abnormality is detected based on the diagnosissignal Sd output by the diagnosis unit 67.

Effect of the First Embodiment

(1) The first sensor 33 and the second sensor 34 output the first sensorsignal and the second sensor signal in accordance with the rotation ofthe motor rotation shaft 21 of the motor 20. The angular positioncalculation unit 61 calculates the angular position information thatrepresents the angular position of the motor rotation shaft 21 based onthe first sensor signal. The rotation number detection unit 58 detectsthe rotation number of the motor rotation shaft 21 based on the secondsensor signal and outputs the rotation number information representingthe rotation number. The rotation angle information calculation unit 66calculates rotation angle information representing the rotation angle ofthe motor rotation shaft 21 based on the angular position informationand the rotation number information.

The regulator 51, the first power supply unit 52, the second powersupply unit 53, the third power supply unit 54, and the power controlunit 56 provide power to the first sensor 33, the second sensor 34, theangular position calculation unit 61, the rotation number detection unit58, and the rotation angle information calculation unit 66 when thepower switch is on, and stop providing power to the first sensor 33,angular position calculation unit 61, and the rotation angle informationcalculation unit 66 and provide power to the second sensor 34 and therotation number detection unit 58 when the power switch is off.

As a result, in the period when the power switch is off, the powerconsumption in the first sensor 33 and the angular position calculationunit 61 and the rotation angle information calculation unit 66 thatprocess its output signal can be stopped. Therefore, the powerconsumption in the period when the power switch is off can be reduced.

(2) The rotation number detection unit 58 may continue detecting therotation number of the motor rotation shaft 21 while the power switch isoff. The rotation angle information calculation unit 66 may calculatethe rotation angle information based on the rotation number informationoutput by the rotation number detection unit 58 and the angular positioninformation calculated by the angular position calculation unit 61 whenthe power switch is turned on from off.

As a result, in the period when the power switch is off, when the motorrotation shaft 21 is turned by an external force, etc., at the timingwhen the power switch is turned on from off, the rotation angle of themotor rotation shaft 21 in the angle range of multiple turns can becalculated.

(3) The first quadrant information calculation unit 63 a calculates thefirst quadrant information representing which of the quadrants formed bydividing the rotation range of the motor rotation shaft 21 by n theangular position of the motor rotation shaft 21 belongs to based on theangular position information (n is a natural number equal to or greaterthan 2). The second quadrant information calculation unit 63 bcalculates the second quadrant information representing which of thequadrants formed by dividing the rotation range of the motor rotationshaft 21 by n the angular position of the motor rotation shaft 21belongs to based on the rotation number information representing therotation number in the unit of 1/n rotation. The correction unit 63 dcorrects the rotation number information in accordance with thecomparison result of the first quadrant information and the secondquadrant information.

The correction unit 63 d may correct the rotation number information bysubtracting the difference obtained by subtracting the first quadrantinformation from the second quadrant information from the rotationnumber information.

As a result, even when an error occurs to the rotation numberinformation calculated by the second sensor signal, the error in therotation number information can be corrected based on the angularposition information calculated based on the first sensor signal.Consequently, the accuracy of the rotation angle information can beimproved.

(4) The above-mentioned natural number n is 4, and the second sensorsignal is the second sine-wave signal sin 2 and the second cosine-wavesignal cos 2 in accordance with the rotation of the motor rotation shaft21. The rotation number detection unit 58 may detect the rotation numberbased on the change of the combination of the signs of the secondsine-wave signal sin 2 and the second cosine-wave signal cos 2.

As a result, the rotation number representing the rotation number in theunit of ¼ rotation can be detected using a sensor that outputs asine-wave signal and a cosine-wave signal in accordance with therotation of the motor rotation shaft 21.

(5) The electric power steering device of the embodiment includes atorque sensor 10 that detects the steering torque applied to thesteering shaft based on the torsion angle of the input shaft 2 i and theoutput shaft 2 o that are connected via the torsion bar mounted on thesteering shaft of the vehicle, the motor 20 that is connected to theoutput shaft 2 o via the reduction gear 3 and applies the steeringassistance force to the steering shaft, the rotation angle informationcalculation unit 66 that calculates the rotation angle information ofthe motor rotation shaft 21 of the motor 20, and the assist control unit68 that drives and controls the motor 20 based on the steering torque.The rotation angle information calculation unit 66 calculates thesteering angle of the input shaft 2 i based on the torsion angle, thereduction ratio of the reduction gear 3, and the rotation angleinformation.

In this way, the steering angle of the steering shaft can be detectedusing the rotation angle information of the motor rotation shaft 21 ofthe motor 20 without installing an angle sensor that detects thesteering angle of the steering shaft. For example, the steeringassistance force applied to the steering shaft by the motor 20 can becontrolled based on the steering angle calculated by the rotation angleinformation calculation unit 66.

Second Embodiment

A power management unit 50 according to the second embodiment isdescribed. The power management unit 50 of the second embodimentgenerates an internal power source Vp (refer to FIG. 14 ) for driving adigital logical circuit inside the power management unit 50 in additionto the first sensor power source Vs1, the second sensor power sourceVs2, and the power source Vm based on the ignition key signal IG fromthe power supplied from the battery 14.

While the ignition key 11 is on, the power management unit 50 suppliespower source Vm to the MPU 60, etc. in a similar manner to the firstembodiment.

While the ignition key 11 is on, the power management unit 50 suppliesthe first sensor power source Vs1 and the second sensor power source Vs2to the first sensor 33 and the second sensor 34, respectively. Thevoltage of the first sensor power source Vs1 and the second sensor powersource Vs2 while the ignition key 11 is on may be the common powervoltage Vcc1 (Vcc1=5 V, for example), for example.

The power management unit 50 continually supplies the internal powersource Vp to the logical circuit inside the power management unit 50,regardless of whether the ignition key 11 is on or off.

On the other hand, the power management unit 50 stops providing thefirst sensor power source Vs1 and the power source Vm to the firstsensor 33 and the MPU 60, etc. while the ignition key 11 is off. Thepower management unit 50 supplies the second sensor power source Vs2 tothe second sensor 34 intermittently.

For example, the voltage of the second sensor power source Vs2 that issupplied intermittently while the ignition key 11 is off may be thepower voltage Vcc2 that is lower than the power voltage Vcc1. The powervoltage Vcc2 may be 3.3 V, for example.

Refer to FIG. 6A and FIG. 6B. As described above, the threshold voltageVr is set to one-half of the second sensor power source Vs2 (in otherwords, Vs2/2). Therefore, for example, when the ignition key 11 is onand the second sensor power source Vs2 is 5 V, the threshold voltage Vrmay be set to 2.5 V, and when the ignition key 11 is off and the secondsensor power source Vs2 is 3.3 V, the threshold voltage Vr may be set to1.65 V.

FIG. 14 is a block diagram of an exemplary functional configuration of apower management unit 50 of the second embodiment. A component similarto that of the power management unit 50 of the first embodiment isindicated with the same reference sign. A power management unit 50 ofthe second embodiment includes an internal power generation unit 55 anda sensor power determination unit 57.

The third power supply unit 54 is an example of a “sensor power supplyunit”. The first power supply unit 52, the second power supply unit 53and the internal power generation unit 55 are an example of a “powersupply unit” described in the claims.

The power control unit 56 generates an operation switching signal Sigbased on the ignition key signal IG and outputs to the regulator 51, thefirst power supply unit 52, the second power supply unit 53, and thethird power supply unit 54.

The operation switching signal Sig has a different value in accordancewith whether the ignition key 11 is on or off.

In other words, the operation switching signal Sig represents whetherthe ignition key 11 is on or off. For example, the value representingthat the ignition key 11 is on may be “1”, and the value representingthat the ignition key 11 is off may be “0”.

The power control unit 56 generates a drive interval instruction signalSi and outputs to the third power supply unit 54. The drive intervalinstruction signal Si is a signal that indicates the interval ofintermittently supplying power to the second sensor while the ignitionkey 11 is off, in other words, a signal that indicates the driveinterval of driving the second sensor 34. The details of the powercontrol unit 56 will be described later.

The regulator 51 generates regulator power source VR having apredetermined voltage from the battery power source Vbat. The firstpower supply unit 52, the second power supply unit 53, the third powersupply unit 54, and the internal power generation unit 55 generate thepower source Vm, the first sensor power source Vs1, the second sensorpower source Vs2, and the internal power source Vp respectively from theregulator power source VR.

The regulator 51 switches the voltage of the regulator power source VRin accordance with the operation switching signal Sig. For example, thevoltage of the regulator power source VR while the operation switchingsignal Sig is “1” (in other words, while the ignition key 11 is on) maybe 6 V, and the voltage of the regulator power source VR while theoperation switching signal Sig is “0” (in other words, while theignition key 11 is off) may be 4 V.

The first power supply unit 52 continually supplies power source Vm tothe MPU 60, etc. while the operation switching signal Sig has the valueof “1”.

While the operation switching signal Sig has the value of “1”, thesecond power supply unit 53 continually supplies the first sensor powersource Vs1 to the first sensor 33, and the third power supply unit 54continually supplies the second sensor power source Vs2 to the secondsensor 34.

As a result, in the period while the ignition key 11 is on, the MPU 60,etc., the first sensor 33 and the second sensor 34 operate continually.The voltages of the first sensor power source Vs1 and the second sensorpower source Vs2 are the common power voltage Vcc1.

On the other hand, when the operation switching signal Sig has a valueof “0” (in other words, while the ignition key 11 is off), the firstpower supply unit 52 and the second power supply unit 53 stop generatingthe power source Vm and the first sensor power source Vs1. Accordingly,the supply of the first sensor power source Vs1 to the first sensor 33and the supply of the power source Vm to the MPU 60, etc. are stopped,and the operation of the first sensor 33 and the MPU 60, etc. stops.

The third power supply unit 54 generates the second sensor power sourceVs2 having the power voltage Vcc2 that is lower than the power voltageVcc1 while the operation switching signal Sig has a value of “0”. Thethird power supply unit 54 intermittently generates the second sensorpower source Vs2 in the drive interval instructed by the drive intervalinstruction signal Si while the operation switching signal Sig has avalue of “0”.

As a result, the second sensor power source Vs2 having a power voltageVcc2 that is lower than the power voltage Vcc1 is intermittentlysupplied to the second sensor 34, and the second sensor 34 operatesintermittently.

The internal power generation unit 55 supplies the internal power sourceVp to the rotation number detection unit 58 regardless of the value ofthe operation switching signal Sig being “1” or “0” (regardless of theignition key 11 being on or off).

The sensor power determination unit 57 determines whether the secondsensor power source Vs2 is supplied to the second sensor 34 in theperiod when the ignition key 11 is off (in other words, the period inwhich the second sensor power source Vs2 is generated intermittently).The sensor power determination unit 57 generates an activation signal Srfor operating the rotation number detection unit 58 at the timing whenthe second sensor power source Vs2 is supplied to the second sensor 34.The value of the activation signal Sr intermittently becomes “1” in theperiod when the second sensor power source Vs2 is supplied, and becomes“0” in the period when the second sensor power source Vs2 is notsupplied, for example.

While the ignition key 11 is on, the rotation number detection unit 58continually operates. While the ignition key 11 is off, the rotationnumber detection unit 58 operates when the value of the activationsignal Sr from the sensor power determination unit 57 is “1” (in otherwords, the second sensor power source Vs2 is supplied to the secondsensor 34). Therefore, the rotation number detection unit 58 operatesintermittently.

The first comparator 58 a and the second comparator 58 b of the rotationnumber detection unit 58 operate intermittently while the ignition key11 is off, and changes the sign signals Cs and Cc in accordance with theresult of comparing the second sine-wave signal sin 2 and the secondcosine-wave signal cos 2 and the threshold voltage Vr. In the periodwhen the second sensor power source Vs2 is not supplied to the secondsensor 34, the internal power source Vp maintains the output of the signsignals Cs and Cc. The sine counter 58 c and the cosine counter 58 doperate using the internal power source Vp as the power source andcalculate the sine count value CNTs and the cosine count value CNTc,respectively.

The power control unit 56 is further described. As described above, thepower control unit 56 controls the regulator 51, the first power supplyunit 52, the second power supply unit 53, and the third power supplyunit 54 by generating the operation switching signal Sig and the driveinterval instruction signal Si. The power control unit 56 includes anaction switching unit 56 a and a drive interval changing unit 56 b.

The action switching unit 56 a generates the operation switching signalSig based on the ignition key signal IG.

The drive interval changing unit 56 b generates the drive intervalinstruction signal Si based on whether the rotation of the motorrotation shaft 21 is detected or not. As described above, the driveinterval instruction signal Si instructs the drive interval forintermittently driving the second sensor 34.

The drive interval changing unit 56 b expands/shortens the driveinterval instructed by the drive interval instruction signal Si inaccordance with whether the rotation of the motor rotation shaft 21 isdetected or not.

More specifically, the drive interval changing unit 56 b shortens thedrive interval instructed by the drive interval instruction signal Sifrom the predetermined maximum interval x when a rotation of the motorrotation shaft 21 is detected and expands the drive interval to themaximum interval x when a rotation of the motor rotation shaft 21 is nolonger detected afterwards. The maximum interval x is an example of the“first time interval”.

As described above, by shortening the drive interval for intermittentlydriving the second sensor 34 when a rotation of the motor rotation shaft21 is detected, a counting mistake of the sine count value CNTs and thecosine count value CNTc can be prevented.

For example, the drive interval changing unit 56 b may generate thedrive interval instruction signal Si in accordance with whether a changein the second sine-wave signal sin 2 and the second cosine-wave signalcos 2 is detected or not.

More specifically, the drive interval changing unit 56 b generates thedrive interval instruction signal Si based on the change of the signsignal Cs of the second sine-wave signal sin 2 that is the output of thefirst comparator 58 a and the change of the sign signal Cc of the secondcosine-wave signal cos 2 that is the output of the second comparator 58b.

In other words, the drive interval changing unit 56 b shortens the driveinterval instructed by the drive interval instruction signal Si from themaximum interval x when a change occurs in the sign signals Cs and Cc.

Afterwards, the drive interval changing unit 56 b expands the driveinterval instructed by the drive interval instruction signal Si to themaximum interval x when a change no longer occurs to the sign signals Csand Cc.

For example, the drive interval changing unit 56 b may start to expandthe drive interval when the change of neither of the sign signals Cs andCc is detected even when the power is supplied intermittently for thepredetermined multiple times to the second sensor 34.

When the drive interval changing unit 56 b detects a change in one ofthe sign signals Cs and Cc and then detects a change in the other of thesign signals Cs and Cc, the drive interval instructed by the driveinterval instruction signal Si may be shortened by steps.

For example, when a change in one of the sign signals Cs and Cc isdetected, the drive interval changing unit 56 b shortens the driveinterval by the predetermined length T1, and when a change in the othersignal is detected afterwards, further shortens the drive interval bythe predetermined length T1. Therefore, the shortening length changes bysteps of T1, (2×T1).

By shortening the drive interval by steps as described above, a countingmistake of the sine count value CNTs and the cosine count value CNTc canbe prevented while suppressing the increase in the power consumption dueto the shortening of the drive interval.

Referring to FIG. 15A to FIG. 15C, an example of controlling the driveinterval of the second sensor 34 when a rotation of the motor rotationshaft 21 is detected while the ignition key 11 is off is described. FIG.15A illustrates an example when the predetermined length T1 is 2.2 msec.The initial drive interval is the maximum interval x, and as representedby the reference sign 100, when the sign signal Cs changes from “0” to“1”, the drive interval is shortened from the maximum interval x to(x−2.2) msec.

Then, when the sign signal Cc changes from “0” to “1” as represented bythe reference sign 101, the drive interval is shortened from (x−2.2)msec to (x−4.4) msec. For example, when the maximum interval x is 6.6msec, the drive interval instructed by the drive interval instructionsignal Si is shortened by steps from 6.6 msec to 4.4 msec, and then to2.2 msec.

When the drive interval instructed by the drive interval instructionsignal Si is shortened to a predetermined minimum interval, the driveinterval changing unit 56 b prohibits shortening the drive interval to avalue shorter than the minimum interval even when a change in the signsignals Cs and Cc is detected. For example, in the example in FIG. 15A,the minimum interval may be (x−4.4) msec. In the example in FIG. 15A,when the maximum interval x is 6.6 msec, the minimum interval becomes2.2 msec.

The time width w of the period when the second sensor power source Vs2is supplied to the second sensor 34 (in other words, the period when thesecond sensor 34 is driven) may be fixed. The time width w may be 220μsec, for example.

When the time width w is fixed, the duty ratio of the drive period ofthe second sensor 34 when the drive interval is the maximum interval of6.6 msec is ⅓ of when the drive interval is the minimum interval of 2.2msec.

When the time width w is 220 μsec and the drive interval is the minimuminterval of 2.2 msec, the duty ratio is 10%.

There is a case when one of the sign signals Cs and Cc changes, and thenbefore the other of the sign signals Cs and Cc changes, the one of thesign signals Cs and Cc changes again.

In the example in FIG. 15B and FIG. 15C, as represented by the referencesign 100, when the sign signal Cs changes from “0” to “1”, and then thesign signal Cs returns to “0” from “1” although the sign signal Cc doesnot change from “0” to “1”.

Such an event occurs when the motor rotation shaft 21 rotates and one ofthe sign signals Cs and Cc changes, and then the motor rotation shaft 21does not rotate to the same direction for more than 90 degrees, butrotates to the opposite direction, for example.

In this case, the motor rotation shaft 21 is not rotating fast so thereis a little risk of a counting mistake of the sine count value CNTs andthe cosine count value CNTc even if the drive interval is not greatlyshortened.

Accordingly, the drive interval changing unit 56 b may be configured notto shorten the drive interval instructed by the drive intervalinstruction signal Si when one of the sign signals Cs and Cc changes,and then before the other of the sign signals Cs and Cc changes, the oneof the sign signals Cs and Cc changes again.

For example, the drive interval changing unit 56 b stores the changehistory of the sign signal Cs representing the change of the sign signalCs when a change in the sign signal Cs is detected.

When the change history of the sign signal Cs is stored and a change inthe sign signal Cs is detected, the drive interval changing unit 56 bdoes not shorten the drive interval by steps. On the contrary, when thechange history of the sign signal Cs is not stored and a change in thesign signal Cs is detected, the drive interval changing unit 56 bshortens the drive interval and stores the change history of the signsignal Cs.

When the change history of the sign signal Cs is stored and a change inthe sign signal Cc is detected, the drive interval changing unit 56 bshortens the drive interval and stores the change history of the signsignal Cc. At this time, the drive interval changing unit 56 b resetsthe change history to a state in which the change of the sign signal Csis not stored.

When the change history of the sign signal Cc is stored and a change inthe sign signal Cc is detected, the drive interval changing unit 56 bdoes not shorten the drive interval by steps.

On the contrary, when the change history of the sign signal Cc is notstored and a change in the sign signal Cc is detected, the driveinterval changing unit 56 b shortens the drive interval by steps andstores the change history of the sign signal Cc.

When the change history of the sign signal Cc is stored and a change inthe sign signal Cs is detected, the drive interval changing unit 56 bshortens the drive interval and stores the change history of the signsignal Cs. The drive interval changing unit 56 b resets the changehistory to a state in which the change of the sign signal Cc is notstored.

The change history of the sign signals Cs and Cc may be stored by aflip-flop circuit, etc. when the drive interval changing unit 56 b isimplemented by hardware such as a logical circuit for example.

The change history of the sign signals Cs and Cc may be stored by aflag, etc. when the drive interval changing unit 56 b is realized bysoftware.

Next, the operation of the drive interval changing unit 56 b when therotation of the motor rotation shaft 21 is not detected while theignition key 11 is off is described.

As described above, the drive interval changing unit 56 b expands thedrive interval instructed by the drive interval instruction signal Si tothe maximum interval x when a change no longer occurs to the signsignals Cs and Cc after the drive interval instructed by the driveinterval instruction signal Si is shortened.

More specifically, when a change in neither of the sign signals Cs andCc is detected even when power is intermittently supplied to the secondsensor 34 for predetermined multiple times, the drive intervalinstructed by the drive interval instruction signal Si is expanded tothe maximum interval x.

Therefore, the drive interval changing unit 56 b counts the power supplycount CNTr that represents the number of times that power isintermittently supplied to the second sensor 34 after the last detectionof the change of one of the sign signals Cs and Cc.

In other words, the drive interval changing unit 56 b increases thepower supply count CNTr by 1 every time power is intermittently suppliedto the second sensor 34 and resets the power supply count CNTr to 0 whena change in one of the sign signals Cs and Cc is detected.

The drive interval changing unit 56 b determines whether the powersupply count CNTr is equal to or greater than a predetermined countthreshold value Cth or not. When the power supply count CNTr is equal toor greater than the predetermined count threshold value Cth, the driveinterval changing unit 56 b expands the drive interval instructed by thedrive interval instruction signal Si by a predetermined length T2 everytime the power supply count CNTr increases by 1. The predeterminedlength T2 may be shorter than the above-described predetermined lengthT1, or may be equal to the predetermined length T1.

At this time, the drive interval changing unit 56 b resets the changehistory to a state in which the change of the sign signals Cs and Cc isnot stored.

The drive interval changing unit 56 b continues to expand the driveinterval until the drive interval reaches the maximum interval x, andwhen the drive interval reaches the maximum interval x, stops expandingthe drive interval.

Referring to FIG. 16A to FIG. 16D, an example of controlling the driveinterval of the second sensor 34 when a rotation of the motor rotationshaft 21 is not detected while the ignition key 11 is off is described.In the example in the FIG. 16A to FIG. 16D, the count threshold valueCth is 4, and the predetermined length T2 is 1.1 msec.

Now, as illustrated in FIG. 16A, assume that the drive intervalinstructed by the drive interval instruction signal Si is initiallyshortened to (x−4.4) msec.

As represented by the reference sign 102, when the sign signal Cschanges, the drive interval changing unit 56 b resets the power supplycount CNTr to 0. Then, the drive interval changing unit 56 b increasesthe power supply count CNTr by 1 every time power is intermittentlysupplied to the second sensor 34 when no change of either of the signsignals Cs and Cc is detected.

The drive interval changing unit 56 b determines whether or not thepower supply count CNTr is equal to or greater than 4 which is the countthreshold value Cth.

When the power supply count CNTr reaches 4, the drive interval changingunit 56 b expands the drive interval instructed by the drive intervalinstruction signal Si by the predetermined length T2 of 1.1 msec. As aresult, the drive interval expands from (x−4.4) msec to (x−3.3) msec.Then, the drive interval changing unit 56 b expands the drive intervalby 1.1 msec every time the power supply count CNTr increases by 1.

Afterwards, when the drive interval instructed by the drive intervalinstruction signal Si is expanded to the maximum interval x, the driveinterval changing unit 56 b stops expanding the drive interval.

Here, the numerical examples of the above-described predeterminedlengths T1 and T2, the maximum interval x and the minimum interval ofthe drive interval, and the count threshold value Cth are merelyexamples, and the present invention is not limited to the abovenumerical examples. The value of the predetermined length T1, themaximum interval x and the minimum interval may be set appropriately inaccordance with the actual device configuration.

When the drive interval becomes shorter than the minimum interval whenthe drive interval is shortened by the predetermined length T1 when achange in the sign signal Cs or Cc is detected, the drive intervalchanging unit 56 b may shorten the length of shortening the driveinterval to be shorter than the predetermined length T1. Similarly, whenthe drive interval becomes longer than the maximum interval x when thedrive interval is expanded by the predetermined length T2 when no changein the sign signal Cs or Cc is detected, the drive interval changingunit 56 b may shorten the length to expand the drive interval to beshorter than the predetermined length T2.

For example, assume that a change in the sign signal Cs or Cc isdetected at a timing when the drive interval is (x−3.3) msec during theprocess of expanding the drive interval when the predetermined length T1is 2.2 msec and the minimum interval is (x−4.4) msec.

At this time, if the drive interval is shortened by the predeterminedlength T1, the drive interval becomes (x−5.5) msec that is shorter thanthe minimum interval (x−4.4) msec. Therefore, the drive intervalchanging unit 56 b shortens the drive interval by 1.1 msec that isshorter than the predetermined length T1=2.2 msec, and sets the driveinterval to be the minimum interval of (x−4.4) msec.

With reference to FIG. 17 , an example of a method of setting the driveinterval instructed by the drive interval instruction signal Si isdescribed.

In step S1, the sensor power determination unit 57 determines whether arise of the voltage of the second sensor power source Vs2 is detected ornot. When the rise of the voltage of the second sensor power source Vs2is detected (step S1: Y), the process proceeds to step S2. When the riseof the voltage of the second sensor power source Vs2 is not detected(step S1: N), the process terminates. In this case, the drive intervaldoes not change.

In step S2, the sensor power determination unit 57 generates theactivation signal Sr and outputs to the rotation number detection unit58. In the rotation number detection unit 58 started by the activationsignal Sr, the first comparator 58 a and the second comparator 58 boutput the sign signal Cs of the second sine-wave signal sin 2 and thesign signal Cc of the second cosine-wave signal cos 2.

The drive interval changing unit 56 b performs a rotation detectionprocess, and determines whether a rotation of the motor rotation shaft21 is detected or not based on the sign signals Cs and Cc.

With reference to FIG. 18 , an example of the rotation detection processin step S2 is described.

In step S20, the drive interval changing unit 56 b determines whetherthe sign signal Cs changed or not. When the sign signal Cs changed (stepS20: Y), the process proceeds to S21. When the sign signal Cs did notchange (step S20: N), the process proceeds to S25.

In step S21, the drive interval changing unit 56 b determines whetherthe change history of the sign signal Cs representing that the signsignal Cs changed exists or not. When the change history exists (stepS21: Y), the process proceeds to S24. When the change history does notexist (step S21: N), the process proceeds to S22.

In step S22, the drive interval changing unit 56 b stores the changehistory of the sign signal Cs representing that the sign signal Cschanged. The drive interval changing unit 56 b resets the change historyrepresenting the sign signal Cc changed to a state that the change ofthe sign signal Cc is not stored.

In step S23, the drive interval changing unit 56 b determines that arotation of the motor rotation shaft 21 is detected, and terminates therotation detection process.

On the other hand, when the change history is determined not to exist instep s21 (step S21: N), the drive interval changing unit 56 b determinesthat a rotation of the motor rotation shaft 21 is not detected in stepS24, and terminates the rotation detection process.

When the sign signal Cs does not change in step S20 (step S20: N), thedrive interval changing unit 56 b determines whether the sign signal Ccchanged or not in step S25.

When the sign signal Cc changed (step S25: Y), the process proceeds tostep S26. When the sign signal Cc did not change (step S25: N), theprocess proceeds to S24. In this case, the drive interval changing unit56 b determines that a rotation of the motor rotation shaft 21 is notdetected, and terminates the rotation detection process.

In step S26, the drive interval changing unit 56 b determines whetherthe change history of the sign signal Cs representing that the signsignal Cs changed exists or not.

When the change history exists (step S26: Y), the process proceeds toS24. In this case, the drive interval changing unit 56 b determines thata rotation of the motor rotation shaft 21 is not detected, andterminates the rotation detection process.

When the change history of the sign signal Cs does not exist (step S26:N), the process proceeds to S27.

In step S27, the drive interval changing unit 56 b stores the changehistory of the sign signal Cc representing that the sign signal Ccchanged. The drive interval changing unit 56 b resets the change historyrepresenting the sign signal Cs changed to a state that the change ofthe sign signal Cs is not stored.

In step S28, the drive interval changing unit 56 b determines that arotation of the motor rotation shaft 21 is detected, and terminates therotation detection process.

Refer to FIG. 17 . When a rotation of the motor rotation shaft 21 isdetected (step S3: Y), the process proceeds to S4. When a rotation ofthe motor rotation shaft 21 is not detected (step S3: N), the processproceeds to S7.

In step S4, the drive interval changing unit 56 b resets the powersupply count CNTr counting the number of times power is intermittentlysupplied to the second sensor 34.

In step S5, the drive interval changing unit 56 b determines whether thedrive interval instructed by the drive interval instruction signal Si isalready the minimum interval. When the drive interval is the minimuminterval (step S5: Y), the process terminates. In this case, the driveinterval does not change.

When the drive interval is not the minimum interval (step S5: N), theprocess proceeds to step S6.

In step S6, the drive interval changing unit 56 b shortens the driveinterval instructed by the drive interval instruction signal Si.Afterwards, the process terminates.

When a rotation of the motor rotation shaft 21 is not detected in stepS3 (step S3: N), the drive interval changing unit 56 b determineswhether the drive interval instructed by the drive interval instructionsignal Si is the maximum interval x or not in step S7. When the driveinterval is the maximum interval x (step S7: Y), the process terminates.In this case, the drive interval does not change.

When the drive interval is not the maximum interval x (step S7: N), theprocess proceeds to step S8.

In step S8, the drive interval changing unit 56 b determines whether thepower supply count CNTr is equal to or greater than the count thresholdvalue Cth or not.

When the power supply count CNTr is equal to or greater than the countthreshold value Cth (step S8: Y), the process proceeds to S10. When thepower supply count CNTr is not equal to or greater than the countthreshold value Cth (step S8: N), the process proceeds to S9. In thiscase, the drive interval does not change.

In step S9, the drive interval changing unit 56 b increases the powersupply count CNTr by 1. Afterwards, the process terminates.

In step S8, when the power supply count CNTr is equal to or greater thanthe count threshold value Cth (step S8:Y), the drive interval changingunit 56 b expands the drive interval instructed by the drive intervalinstruction signal Si in step S10.

In step S11, the drive interval changing unit 56 b resets the changehistory to a state in which the change of the sign signals Cs and Cc isnot stored. Afterwards, the process terminates after step S9.

Effect of the Second Embodiment

(1) The second sensor 34 outputs the second sensor signal including thesine-wave signal and the cosine-wave signal in accordance with therotation of the motor rotation shaft 21 of the motor 20. The third powersupply unit 54 supplies the second sensor power source Vs2 to the secondsensor 34. The power control unit 56 controls the third power supplyunit 54 to continually supply the second sensor power source Vs2 to thesecond sensor 34 when the ignition key 11 is on and intermittentlysupply the second sensor power source Vs2 to the second sensor 34 whenthe ignition key 11 is off. The first comparator 58 a and the secondcomparator 58 b detect a change in the sine-wave signal and a change inthe cosine-wave signal.

The power control unit 56 sets a drive interval for driving the secondsensor 34 by providing the second sensor power source Vs2 intermittentlyto the second sensor 34 to a first time interval when no change isdetected in the sine-wave signal and the cosine-wave signal, sets to thesecond time interval that is shorter than the first time interval when achange in only one of the sine-wave signal and the cosine-wave signal isdetected and sets to the third time interval that is shorter than thesecond time interval when a change in one of the sine-wave signal andthe cosine-wave signal is detected and then a change in the other isdetected.

As described above, since the second sensor 34 is driven intermittentlywhen the ignition key 11 is off, the power consumption while theignition key 11 that is the power switch is off can be reduced.

Moreover, since the drive interval of the second sensor 34 is shortenedin accordance with the change of the output signal of the second sensor34, a detection mistake of a rotation of the motor rotation shaft 21 canbe prevented.

Moreover, since the drive interval is shortened by steps in accordancewith the change of the output signal of the second sensor 34, adetection mistake of a rotation of the motor rotation shaft 21 can beprevented while suppressing the increase in the power consumption.

(2) The power control unit 56 may expand by steps the drive interval tothe first time interval when a change in neither of the sine-wave signaland the cosine-wave signal is detected even when the second sensor powersource Vs2 is intermittently supplied for a predetermined plurality oftimes while the drive interval is set to be shorter than the first timeinterval.

As described above, the power consumption can be reduced because thedrive interval is expanded when neither the sine-wave signal or thecosine-wave signal is detected.

Moreover, since the drive interval is expanded by steps, the detectionmistake of a rotation of the motor rotation shaft 21 can be preventedwhile suppressing the increase in the power consumption.

(3) The power control unit 56 may increase the duty ratio of the periodduring which the second sensor power source Vs2 is supplied to thesecond sensor 34 by shortening the drive interval.

For example, the duty ratio when the drive interval is the third timeinterval may be 10%.

The duty ratio when the drive interval is the first time interval may beone-third of the duty ratio when the drive interval is the third timeinterval, for example.

Therefore, the power consumption in the period when the ignition key 11is off can be reduced.

(4) The power control unit 56 may lower the voltage of the second sensorpower source Vs2 that is supplied when the ignition key 11 is off thanwhen the ignition key 11 is on.

For example, the voltage of the second sensor power source Vs2 when theignition key 11 is off may be 3.3 V, and the voltage of the secondsensor power source Vs2 when the ignition key 11 is on may be 5 V.

Therefore, the power consumption in the period when the ignition key 11is off can be reduced.

(5) The first sensor 33 outputs the first sensor signal in accordancewith the rotation of the motor rotation shaft 21 of the motor 20. Theangular position calculation unit 61 calculates the angular positioninformation that represents the angular position of the motor rotationshaft 21 based on the first sensor signal. The rotation number detectionunit 58 detects the rotation number of the motor rotation shaft 21 basedon the second sensor signal and outputs the rotation number informationrepresenting the rotation number. The rotation angle informationcalculation unit 66 calculates rotation angle information representingthe rotation angle of the motor rotation shaft 21 based on the angularposition information and the rotation number information.

The second power supply unit 53, the first power supply unit 52, and theinternal power generation unit 55 supply power to the first sensor 33,the angular position calculation unit 61, the rotation number detectionunit 58, and the rotation angle information calculation unit 66. Thepower control unit 56 may control the second power supply unit 53 andthe first power supply unit 52 to supply power to the first sensor 33,the angular position calculation unit 61, and the rotation angleinformation calculation unit 66 when the ignition key 11 is on and tostop supplying power to the first sensor 33, the angular positioncalculation unit 61, and the rotation angle information calculation unit66 when the ignition key 11 is off.

As a result, in the period when the ignition key 11 is off, the powerconsumption in the first sensor 33 and the angular position calculationunit 61 and the rotation angle information calculation unit 66 thatprocess its output signal can be stopped. Therefore, the powerconsumption in the period when the power switch is off can be reduced.

Third Embodiment

A power management unit 50 according to the third embodiment isdescribed. Similar to the second embodiment, the power management unit50 supplies the power source Vm to the MPU 60, etc. while the ignitionkey 11 is on.

The power management unit 50 supplies the first sensor power source Vs1and the second sensor power source Vs2 to the first sensor 33 and thesecond sensor 34, respectively. While the ignition key 11 is on, thepower management unit 50 continually supplies power as the first sensorpower source Vs1 and the second sensor power source Vs2. The voltage ofthe first sensor power source Vs1 and the second sensor power source Vs2while the ignition key 11 is on may be the common power voltage Vcc1(Vcc1=5 V, for example), for example.

While the ignition key 11 is on, the power management unit 50 suppliesthe internal power source Vp that is the continual power source to thelogical circuit inside the power management unit 50. For example, thevoltage of the internal power source Vp while the ignition key 11 is onmay be the common power voltage Vcc1. In other words, the voltage of theinternal power source Vp may be equal to the voltage of the secondsensor power source Vs2.

The power continually supplied as the second sensor power source Vs2 andthe internal power source Vp while the ignition key 11 is on is anexample of the “first power”.

On the other hand, the power management unit 50 stops providing thefirst sensor power source Vs1 to the first sensor 33 and the and thepower source Vm to the MPU 60, etc. while the ignition key 11 is off.

While the ignition key 11 is off, the power management unit 50intermittently supplies power as the second sensor power source Vs2 tothe second sensor 34.

For example, the voltage of the second sensor power source Vs2 that issupplied intermittently while the ignition key 11 is off may be thepower voltage Vcc2 that is lower than the power voltage Vcc1. The powervoltage Vcc2 may be 3.3 V, for example.

The power intermittently supplied as the second sensor power source Vs2while the ignition key 11 is off is an example of the “second power”.

FIG. 19A is a diagram illustrating a waveform of an exemplary secondsensor power source Vs2 that is output intermittently while the ignitionkey 11 is off.

When the ignition key 11 is off, the voltage of the second sensor powersource Vs2 becomes the power voltage Vcc2 in the intermittent outputperiod for the time width Wt that occurs in the output cycle T andbecomes 0 outside the intermittent output period. Similar to the secondembodiment, the power management unit 50 may dynamically change theoutput cycle T. The output cycle T may be from 2.2 msec to 6.6 msec, forexample.

FIG. 19B is a diagram illustrating a waveform of one intermittent outputof the second sensor power source Vs2. The time width Wt of one outputperiod during which the second sensor power source Vs2 is intermittentlyoutput is the total of a waiting period Pw, an idle period Pi and asampling period Ps.

The waiting period Pw is the period during which sampling of the secondsensor signal is prohibited to prevent the voltage fluctuation thatoccurs immediately after the intermittent output of the second sensorpower source Vs2 starts from affecting the second sensor signal of thesecond sensor 34. The waiting period Pw may be a fixed value for exampleand may be an arbitrary value programmable in the power management unit50.

The period length of the idle period Pi and the sampling period Ps arearbitrary values programmable in the power management unit 50. Thesampling period Ps is specified as the period during which the powermanagement unit 50 samples the second sensor signal of the second sensor34 when the ignition key 11 is off.

The period length of the idle period Pi can be programmed to specify thestart of the sampling period Ps, and the period length of the samplingperiod Ps can be programmed to specify the time of the end of theintermittent output of the second sensor power source Vs2.

The length of the time width Wt of the intermittent output of the secondsensor power source Vs2 affects the dark current that flows in thesensor unit 30 and the controller 40 while the ignition key 11 is off.In other words, the length of the time width Wt affects the powerconsumption of the sensor unit 30 and the controller 40 while theignition key 11 is off. The longer the time width Wt, the larger thedark current and the power consumption, and the shorter the time widthWt, the more the dark current and the power consumption are saved.

On the other hand, when the idle period Pi and the sampling period Psare shortened, it becomes difficult to accurately sample the secondsensor signal output from the second sensor 34 that is intermittentlydriven.

For example, when the supply of the second sensor power source Vs2starts, the voltage of the second sensor signal that the controller 40receives from the second sensor 34 changes with a certain time constantfrom 0 to a value in accordance with the magnetic flux applied to thesecond sensor 34. The time constant of the second sensor signal isdetermined by an electric characteristic of the second sensor 34 itselfor impedance of the harness 35 and the input circuit etc., for example.Therefore, when the idle period Pi is excessively small, there is a riskof sampling a signal smaller than the intended second sensor signal.

Thus, it is desirable that the length of the time width Wt of the oneintermittent output of the second sensor power source Vs2 is set inaccordance with the consumption current (dark current) that is allowedfor the sensor unit 30 and the controller 40 while the ignition key 11is off. For example, the time width Wt of one intermittent output by thesecond sensor power source Vs2 may be equal to or smaller than 220 μsec.

The time width Wt of one intermittent output of the second sensor powersource Vs2 is preferable to be set in accordance with a time constant ofthe second sensor signal when an intermittent supply of the secondsensor power source Vs2 starts while the ignition key 11 is off.

For example, it is realistically possible to design the second sensorsignal to be sufficiently large when 100 μsec passes after the output ofthe second sensor power source Vs2 starts (for example, to rise toapproximately 99% of the magnitude of the second sensor signal when thesecond sensor power source Vs2 is continually supplied). Therefore, forexample, the time width Wt of one intermittent output by the secondsensor power source Vs2 may be equal to or greater than 100 μsec.

While the ignition key 11 is off, the power management unit 50continually supplies power as the internal power source Vp as well. Inother words, the power management unit 50 continually supplies power asthe internal power source Vp, regardless of whether the ignition key 11is on or off.

However, while the ignition key 11 is off, the power management unit 50supplies the internal power source Vp having a lower voltage than thevoltage while the ignition key 11 is on.

For example, the voltage of the internal power source Vp while theignition key 11 is off may be equal to the power voltage Vcc2 that isthe voltage of the second sensor power source Vs2 while the ignition key11 is off.

The power continually supplied as the internal power source Vp while theignition key 11 is off is an example of the “third power”.

With reference to FIG. 20 , a functional configuration example of apower management unit 50 is explained. A component similar to that ofthe power management unit 50 of the first embodiment is indicated withthe same reference sign.

The power control unit 56 generates an operation switching signal Sigbased on the ignition key signal IG and outputs to the regulator 51, thefirst power supply unit 52, the second power supply unit 53, and thethird power supply unit 54.

The power control unit 56 outputs a timing signal St having the cycle Trepresenting the start time of the intermittent output period of thesecond sensor power source Vs2 to the third power supply unit 54 and therotation number detection unit 58 while the ignition key 11 is off.

The regulator 51 generates regulator power source VR having apredetermined voltage from the battery power source Vbat. The firstpower supply unit 52 and the second power supply unit 53 generate thepower source Vm and the first sensor power source Vs1 from thisregulator power source VR. The third power supply unit 54 generates thesecond sensor power source Vs2 and the internal power source Vp from theregulator power source VR.

The regulator 51 switches the voltage of the regulator power VR inaccordance with the operation switching signal Sig.

For example, the voltage of the regulator power source VR while theoperation switching signal Sig is “0” (in other words, while theignition key 11 is off) may be lower than the voltage of the regulatorpower source VR while the operation switching signal Sig is “1” (inother words, while the ignition key 11 is on). Consequently, the voltageof the second sensor power source Vs2 and the internal power source Vpwhile the ignition key 11 is off can be lowered than the voltage whilethe ignition key 11 is on.

For example, the voltage of the regulator power source VR while theoperation switching signal Sig is “1” may be 6 V, and the voltage of theregulator power source VR while the operation switching signal Sig is“0” may be 4 V.

While the operation switching signal Sig has the value of “1”, the firstpower supply unit 52 continually supplies power to the MPU 60, etc. asthe power source Vm, and the second power supply unit 53 continuallysupplies power to the first sensor 33 as the first sensor power sourceVs1.

While the operation switching signal Sig has a value of “1”, the thirdpower supply unit 54 continually supplies power to the second sensor 34and the rotation number detection unit 58 as the second sensor powersource Vs2, and continually supplies power to the rotation numberdetection unit 58 as the internal power source Vp.

As a result, in the period while the ignition key 11 is on, the MPU 60,etc., the first sensor 33 and the second sensor 34 operate continually.The voltage of the first sensor power source Vs1, the second sensorpower source Vs2, and the internal power source Vp is the power voltageVcc1.

On the other hand, when the operation switching signal Sig has a valueof “0” (in other words, while the ignition key 11 is off), the firstpower supply unit 52 and the second power supply unit 53 stop generatingthe power source Vm and the first sensor power source Vs1. Accordingly,the supply of the first sensor power source Vs1 to the first sensor 33and the supply of the power source Vm to the MPU 60, etc. stop, and theoperation of the first sensor 33 and the MPU 60, etc. stops.

The third power supply unit 54 intermittently outputs power having avoltage of power voltage Vcc2 as the second sensor power source Vs2while the operation switching signal Sig has a value of “0”.

As a result, the second sensor power source Vs2 having a power voltageVcc2 that is lower than the power voltage Vcc1 is intermittentlysupplied to the second sensor 34, and the second sensor 34 operatesintermittently.

The third power supply unit 54 intermittently outputs the second sensorpower source Vs2 in the timing based on the timing signal St output bythe power control unit 56. The third power supply unit 54 sets the timewidth Wt of one intermittent output of the second sensor power sourceVs2 in accordance with the waiting period Pw and idle period Pi andsampling period Ps that are preliminarily programmed in the powermanagement unit 50.

The third power supply unit 54 continually generates power having avoltage of power voltage Vcc2 as the internal power source Vp while theoperation switching signal Sig has a value of “0”. For example, whilecontinually generating common power having a voltage of the powervoltage Vcc2 from the regulator power source VR and outputting thecommon power as it is as the internal power source Vp, third powersupply unit 54 may generate the second sensor power source Vs2 byswitching the common power.

While the ignition key 11 is on, the rotation number detection unit 58generates the rotation number information in a predetermined samplingperiod that is shorter than the intermittent output cycle T of thesecond sensor power source Vs2. While the ignition key 11 is off, therotation number detection unit 58 intermittently generates the rotationnumber information when the second sensor power source Vs2 is suppliedto the second sensor 34 in the intermittent output cycle T.

The first comparator 58 a operates using the second sensor power sourceVs2 as the power source and generates a sign signal Cs representing theplus/minus sign of the second sine-wave signal sin 2 by comparing thesecond sine-wave signal sin 2 and the threshold voltage Vr. The signsignal Cs has a logical value of “1” when the second sine-wave signalsin 2 is equal to or greater than the threshold voltage Vr and has alogical value of “0” when the second sine-wave signal sin 2 is less thanthe threshold voltage Vr.

The threshold voltage Vr may be set based on the voltage of the secondsensor power source Vs2. The rotation number detection unit 58 mayinclude a voltage-dividing resistor that generates a threshold voltageVr by dividing the voltage of the second sensor power source Vs2 or theregulator power source VR, for example.

For example, when the ignition key 11 is on and the second sensor powersource Vs2 is 5 V, the threshold voltage Vr may be set to 2.5 V, andwhen the ignition key 11 is off and the second sensor power source Vs2is 3.3 V, the threshold voltage Vr may be set to 1.65 V.

The second comparator 58 b operates using the second sensor power sourceVs2 as the power source and generates a sign signal Cc representing theplus/minus sign of the second cosine-wave signal cos 2 by comparing thesecond cosine-wave signal cos 2 and the threshold voltage Vr. The signsignal Cc has a logical value of “1” when the second cosine-wave signalcos 2 is equal to or greater than the threshold voltage Vr and has alogical value of “0” when the second cosine-wave signal cos 2 is lessthan the threshold voltage Vr.

While the ignition key 11 is off, the first comparator 58 a and thesecond comparator 58 b obtain the second sine-wave signal sin 2 and thesecond cosine-wave signal cos 2 during the sampling period Ps thatstarts from the start time determined based on the timing signal Sthaving a cycle T output from the power control unit 56, the waitingperiod Pw, and the idle period Pi preliminarily programmed in the powermanagement unit 50. As a result, the first comparator 58 a and thesecond comparator 58 b operate intermittently while the ignition key 11is off, and changes the sign signals Cs and Cc in accordance with theresult of comparing the second sine-wave signal sin 2 and the secondcosine-wave signal cos 2 and the threshold voltage Vr.

The sine counter 58 c and the cosine counter 58 d operate using theinternal power source Vp as the power source and calculate the sinecount value CNTs and the cosine count value CNTc, respectively.

The power management unit 50 may dynamically change the intermittentoutput cycle T of the second sensor power source Vs2 while the ignitionkey 11 is off, in a similar manner to the second embodiment. Forexample, when the motor rotation shaft 21 rotates while the ignition key11 is off, afterwards, the motor rotation shaft 21 may rotate faster,and there is a risk that the rotation number detection unit 58 cannotdetect the rotation of the motor rotation shaft 21 correctly. On theother hand, while the motor rotation shaft 21 continues to stop, thepower consumption can be reduced by expanding the intermittent outputcycle T.

Therefore, the power management unit 50 may shorten the intermittentoutput cycle T when a change in one of the second sine-wave signal sin 2or the second cosine-wave signal cos 2 is detected, for example. Also,the power management unit 50 may expand the intermittent output cycle Twhen a period in which no change in either the second sine-wave signalsin 2 or the second cosine-wave signal cos 2 is detected continues.

The configuration example of the power management unit 50 described inreference to FIG. 19A, FIG. 19B, and FIG. 20 includes the first powersupply unit 52 that supplies power source Vm to the MPU 60, etc. and thesecond power supply unit 53 that supplies the first sensor power sourceVs1 to the first sensor 33, however, the present invention is notlimited to such a configuration. The power source Vm and the firstsensor power source Vs1 may be supplied from a component other than thepower management unit 50 so long as they are supplied when the ignitionkey 11 is on and the supply stops when the ignition key 11 is off.

Effect of the Third Embodiment

(1) The rotation angle detection device of the third embodiment includesthe first sensor 33 that is supplied with power when the ignition key 11is on and outputs the first sensor signal in accordance with therotation of the motor rotation shaft 21 of the motor 20, power supplyfor the the first sensor 33 being stopped when the ignition key 11 isoff, the angular position calculation unit 61 that is supplied withpower when the ignition key 11 is on and calculates the angular positioninformation representing the angular position of the motor rotationshaft 21 based on the first sensor signal, power supply for the angularposition calculation unit 61 being stopped when the ignition key 11 isoff, the second sensor 34 that outputs the second sensor signalincluding the sine-wave signal and the cosine-wave signal in accordancewith the rotation of the motor rotation shaft 21, the power managementunit 50 that continually supplies the first power to the second sensor34 when the ignition key 11 is on, and intermittently supplies thesecond power having a voltage lower than the first power to the secondsensor 34 when the ignition key 11 is off and outputs rotation numberinformation representing the rotation number of the motor rotation shaftbased on the second sensor signal, and the rotation angle informationcalculation unit 66 that is supplied with power when the ignition key 11is on, and calculates the rotation angle information representing therotation angle of the motor rotation shaft 21 based on the angularposition information and the rotation number information, the powersupply for the angle information calculation unit 66 being stopped whenthe ignition key 11 is off.

The power management unit 50 includes the third power supply unit 54that generates the first power and the second power, the comparators 58a and 58 b that operate using the first power supplied from the thirdpower supply unit 54 as the power source and compare the first referencevoltage based on the voltage of the first power and the second sensorsignal when the ignition key 11 is on, and operate using the secondpower as the power source supplied from the third power supply unit 54and compare the second reference voltage based on the voltage of thesecond power and the second sensor signal when the ignition key 11 isoff, and counters 58 c and 58 d that detect the rotation number of themotor rotation shaft by counting the outputs of the comparators 58 a and58 b.

As described above, since the second sensor 34 and comparators 58 a and58 b are driven intermittently and these power voltages are lowered whenthe ignition key 11 is off, the power consumption while the ignition key11 is off can be reduced.

Moreover, by arranging the comparators 58 a and 58 b that acquire thesecond sensor signal of the second sensor 34 that is intermittentlydriven in the power management unit 50 that intermittently outputs thepower source of the second sensor 34, the operation of comparators 58 aand 58 b can be more easily synchronized with the intermittent drivingof the second sensor 34.

By driving the comparators 58 a and 58 b with the same power source asthat of the second sensor 34, and setting the reference voltage forcomparing with the second sensor signal based on the voltage of thepower source of the second sensor 34, the proper outputs of thecomparators 58 a and 58 b can be obtained even if the power voltage forthe second sensor 34 switches as the ignition key 11 is turned on andoff.

(2) The third power supply unit 54 may supply the first power as thepower source to the counters 58 c and 58 d when the ignition key 11 ison and may generate the third power that is the continuous power havingthe same voltage as the second power and supply to the counters 58 c and58 d when the ignition key 11 is off.

Since the power voltages of the counters 58 c and 58 d are lowered whenthe ignition key 11 is off, the power consumption while the ignition key11 is off can be reduced.

(3) The power management unit 50 includes a regulator 51 that generatesthe fourth power that is continuous power having the first regulatorvoltage from an external power source when the ignition key 11 is on andgenerates fifth power that is continuous power having the secondregulator voltage lower than the first regulator voltage from anexternal power source when the ignition key 11 is off, and the thirdpower supply unit 54 may generate the first power from the fourth powerand may generate the second power and the third power from the fifthpower.

As a result, the output voltage of the third power supply unit 54 can beswitched by switching the output power from the regulator 51.

(4) The comparators 58 a, 58 b, and the third power supply unit 54 canbe arranged in a single integrated circuit chip.

As a result, the operation of the comparators 58 a and 58 b can be moreeasily synchronized with the intermittent driving of the second sensor34.

(5) The time width Wt of one intermittent output of the second power maybe set in accordance with the consumption current acceptable by therotation angle detection device when the ignition key 11 is off.Therefore, the power consumption in the period while the ignition key 11is off can be reduced.

(6) The time width Wt of one intermittent output of the second power maybe set in accordance with the time constant of the second sensor signalwhen the second power is intermittently supplied. As a result, samplingof a signal smaller than the original second sensor signal due to thetime width Wt being too small can be prevented.

(7) The time width of one intermittent output of the second power may beequal to or smaller than 220 ρsec, for example. As a result, the powerconsumption in the period while the ignition key 11 is off can bereduced.

Fourth Embodiment

A sensor unit 30 and a controller 40 according to the fourth embodimentare described. A power management unit 50 intermittently supplies poweras a second sensor power source Vs2 to a second sensor 34 while theignition key 11 is off. However, when the sensor unit 30 is formed as aunit separate from the controller 40, and a second sensor power sourceVs2 is intermittently supplied to a second sensor 34 via a harness 35,transient current may flow right after start, and the power voltage maybecome unstable and electro-magnetic noise may be generated. As aresult, while the ignition key 11 is off, there is a risk that thesecond sensor signal obtained from the second sensor 34 becomesunstable.

Hence, for the sensor unit 30 and the controller 40 according to thefourth embodiment, one or both of a bypass capacitor and a decouplingcapacitor are arranged in the power line of the second sensor powersource Vs2. The bypass capacitor mainly has a function of allowing thenoise element whose frequency is relatively high to escape to theground, and the decoupling capacitor mainly has a function of absorbingthe voltage fluctuation whose frequency is relatively low andstabilizing the power supply system, however, there is a case that onecapacitor has both functions.

FIG. 21 is a block diagram illustrating an outline of an exemplarycircuit configuration of the sensor unit 30 according to the fourthembodiment. The sensor unit 30 includes the first sensor 33, the secondsensor 34, a first amplifier 36, a second amplifier 37, a first offsetvoltage output circuit 38, a second offset voltage output circuit 39,voltage-dividing resistors Rd11, Rd12, Rd21, and Rd22.

A first sensor power line VL1 of the first sensor power source Vs1 and asecond sensor power line VL2 of the second sensor power source Vs2 onthe side of the sensor unit 30 are connected to a first sensor powerline VL1 and a second sensor power line VL2 on the side of the harness35, and the first sensor power source Vs1 and the second sensor powersource Vs2 are supplied from the controller 40. A first sensor groundingline GND1 and a second sensor grounding line GND2 on the side of thesensor unit 30 are connected to a grounding line (not illustrated) onthe controller 40 side via a grounding line GND on the harness 35 side.

The second sensor 34 includes a bridge circuit 34 a of magnetoresistiveelements Rs21, Rs22, Rs23, and Rs24, and a bridge circuit 34 b of themagnetoresistive elements Rc21, Rc22 Rc23, and Rc24.

The magnetization direction of the pin layer of the magnetoresistiveelements Rs21, Rs22, Rs23, and Rs24 and the magnetization direction ofthe pin layer of the magnetoresistive elements Rc21, Rc22 Rc23, and Rc24differ by 90°.

Differential sine-wave signals Ss2 p and Ss2 n representing the sinewave component in accordance with the motor rotation shaft 21 are outputfrom the output terminals SIN 2P and SIN 2N that are connected to themidpoint potential points when the second sensor power source Vs2 issupplied between the connection point of the magnetoresistive elementsRs21 and Rs22 that are connected to the second sensor power line VL2 viathe power terminal V2 SIN and the connection point of themagnetoresistive elements Rs23 and Rs24 that are connected to the secondsensor grounding line GND2 via the grounding terminal G2 SIN.

The differential cosine-wave signals Sc2 p and Sc2 n representing thecosin wave component in accordance with the motor rotation shaft 21 areoutput from the output terminals COS 2P and COS 2N that are connected tothe midpoint potential points when the second sensor power source Vs2 issupplied between the connection point of the magnetoresistive elementsRc21 and Rc22 that are connected to the second sensor power line VL2 viathe power terminal V2 COS and the connection point of themagnetoresistive elements Rc23 and Rc24 that are connected to the secondsensor grounding line GND2 via the grounding terminal G2 COS.

The first sensor 33 has the same configuration as the second sensor 34,and the power terminals V1 SIN and V1 COS correspond to the powerterminals V2 SIN and V2 COS respectively, the grounding terminals G1 SINand G1 COS correspond to the grounding terminals G2 SIN and G2 COSrespectively, the output terminals SIN 1N, SIN 1P, COS 1N, and COS 1Pcorrespond to the output terminals SIN 2N, SIN 2P COS 2N, and COS 2Prespectively, the differential sine-wave signals Ss1 p and Ss1 ncorrespond to the differential sine-wave signals Ss2 p and Ss2 nrespectively, and the differential cosine-wave signals Sc1 p and Sc1 ncorrespond to the differential cosine-wave signals Sc2 p and Sc2 nrespectively.

The second amplifier 37 outputs a second sine-wave signal sin 2 byamplifying the differential sine-wave signals Ss2 p and Ss2 n andapplying an offset voltage Voff2 output from the second offset voltageoutput circuit 39. Also, second amplifier 37 outputs a secondcosine-wave signal cos 2 by amplifying the differential cosine-wavesignals Sc2 p and Sc2 n and applying an offset voltage Voff2. The secondamplifier 37 includes a differential amplifier 37 a having anon-inversion terminal and an inversion terminal to which thedifferential sine-wave signals Ss2 p and Ss2 n are input respectivelyand a differential amplifier 37 b having a non-inversion terminal and aninversion terminal to which the differential cosine-wave signals Sc2 pand Sc2 n are input respectively.

The second offset voltage output circuit 39 applies the offset voltageVoff2 to the non-inversion terminals of differential amplifiers 37 a and37 b.

The second offset voltage output circuit 39 may be a voltage followercircuit having an amplifier 39 a including a non-inversion terminal towhich the division voltage acquired by dividing the second sensor powersource Vs2 by the voltage-dividing resistors Rd21 and Rd22 is input, forexample. For example, the resistance values of the voltage-dividingresistors Rd21 and Rd22 may be equalized, and the second sensor powersource Vs2 may be divided in the ratio of 1:1. In this case, the offsetvoltage Voff2 becomes ½ of the second sensor power source Vs2 (Vs2/2).

The first amplifier 36 and the first offset voltage circuit 38 have thesame configuration as the second amplifier 37 and the second offsetvoltage circuit 39.

The first amplifier 36 outputs a first sine-wave signal sin 1 byamplifying the differential sine-wave signals Ss1 p and Ss1 n andapplying an offset voltage Voff1 output from the first offset voltageoutput circuit 38. Also, the first amplifier 36 outputs a firstcosine-wave signal cos 1 by amplifying the differential cosine-wavesignals Sclp and Sc1 n and applying an offset voltage Voff1.

The first offset voltage output circuit 38 may be a voltage followercircuit to which the division voltage acquired by dividing the firstsensor power source Vs1 by the voltage-dividing resistors Rd11 and Rd12is input, for example. The offset voltage Voff1 may be one-half of thefirst sensor power source Vs1 (Vs1/2), for example.

The first sine-wave signal sin 1, the first cosine-wave signal cos 1,the second sine-wave signal sin 2, and the second cosine-wave signal cos2 are transmitted to the controller 40 via the harness 35.

In both cases when the ignition key 11 is on where the second sensorpower source Vs2 is continually supplied and when the ignition key 11 isoff where the second sensor power source Vs2 is intermittently supplied,the present invention requires (1) power stability on the side of thesecond sensor 34, (2) good Electromagnetic Compatibility (EMC)characteristics, and (3) reducing the dark current when the ignition key11 is off.

From the viewpoint of power stability, a high-capacity decouplingcapacitor is desired. On the other hand, when the ignition key 11 is offwhere the second sensor power source Vs2 is intermittently supplied, asmall-capacity bypass capacitor is desired from the viewpoint of a fastsignal rise and dark current reduction. From the viewpoint of EMCcharacteristics, a bypass capacitor that functions in the high-frequencyregion is desired.

The inventors discovered that a stable second sensor signal can beobtained by arranging a bypass capacitor and a decoupling capacitor atthe following three locations (1) to (3) by repeating simulations.

(1) An Input Terminal of the Second Offset Voltage Output Circuit 39

By arranging a decoupling capacitor C12 to connect the input terminal ofthe second offset voltage output circuit 39 and the second sensorgrounding line GND2 (in other words, the connection point of thevoltage-dividing resistors Rd21 and Rd22 and the second sensor groundingline GND2 are connected), when the second sensor power source Vs2 isintermittently supplied, even when the second sensor power source Vs2 isswitched, the voltage fluctuation in the power source caused by thetransient current is blocked by a low-pass filter formed by thevoltage-dividing resistor Rd21 and the decoupling capacitor C12, andtherefore the fluctuation in the DC component of the second sensorsignal is suppressed. As a result, the stability of the second sensorsignal can be improved.

(2) A Position Proximate to the Second Sensor 34

By arranging bypass capacitors C23 and C24 connecting the second sensorpower line VL2 and the second sensor grounding line GND2 at a positionproximate to the second sensor 34, the effect of the electromagneticnoise occurred by the switching of the second sensor power source Vs2 onthe second sensor 34 is suppressed, and therefore the stability of thesecond sensor signal is improved.

(3) A Position Proximate to the Power Management Unit 50

By arranging a decoupling capacitor C32 (refer to FIG. 22 ) thatconnects the second sensor power line VL2 of the harness 35 and thegrounding line GND at a position in the proximity of the powermanagement unit 50, the entry of the voltage fluctuation that occurswhen the second sensor power source Vs2 is switched into the harness 35is prevented, and therefore the power is supplied by the harness 35 in astable manner. Moreover, noise generated by the harness 35 can bereduced.

When the ignition key 11 is on (in other words, when the second sensorpower source Vs2 is continually supplied), the effect of the noise fromoutside to the second sensor 34 can be suppressed by connecting one orboth of a bypass capacitor and a decoupling capacitor at theabove-described 3 locations (1) to (3), so the stability of the secondsensor signal can be improved.

Similar to the second sensor power line VL2 of the second sensor powersource Vs2, a bypass capacitor and a decoupling capacitor may bearranged on the first sensor power line VL1 of the first sensor powersource Vs1. In the embodiment, a decoupling capacitor C11 (refer to FIG.21 ) that connects the input terminal of the first offset voltage outputcircuit 38 and the first sensor grounding line GND1 is provided.

Bypass capacitors C21 and C22 that connect the first sensor power lineVL1 and the first sensor grounding line GND1 at a position proximate tothe first sensor 33 are also arranged.

A decoupling capacitor C31 (refer to FIG. 22 ) that connects the firstsensor power line VL1 and the grounding line GND of the harness 35 at aposition proximate to the power management unit 50 is arranged.

A bypass capacitor Ce1 that connects the first sensor power line VL1 andthe first sensor grounding line GND1 on the sensor unit 30 side forpreventing electrostatic discharge surge (ESD) and a bypass capacitorCe2 that connects the second sensor power line VL2 and the second sensorgrounding line GND2 on the sensor unit 30 side for ESD prevention may bearranged at a position proximate to the connector with the harness 35.

Effect of the Fourth Embodiment

(1) The rotation angle detection device of the embodiment includes thesensor unit 30 that outputs the first sensor signal including thesine-wave signal and the cosine-wave signal in accordance with therotation of the motor rotation shaft 21 of the motor 20 and the secondsensor signal including a sine-wave signal and a cosine-wave signal inaccordance with the motor rotation shaft 21, the controller 40 thatcalculates the rotation angle information representing the rotationangle of the motor rotation shaft 21 based on the first sensor signaland the second sensor signal while supplying power to the sensor unit30, and the harness 35 that connects the controller 40 and the sensorunit 30, transmits power from the controller 40 to the sensor unit 30,and transmits the first sensor signal and the second sensor signal fromthe sensor unit 30 to the controller 40.

The sensor unit 30 includes the first sensor 33 driven by the firstsensor power source Vs1 supplied by the controller 40 via the harness 35that outputs a sine-wave signal and a cosine-wave signal in accordancewith the rotation of the motor rotation shaft 21, the first amplifier 36that amplifies the output signal of the first sensor 33 and outputs asthe first sensor signal, the second sensor 34 that is driven by thesecond sensor power source Vs2 supplied by the controller 40 via theharness 35 and outputs a sine-wave signal and a cosine-wave signal inaccordance with the rotation of the motor rotation shaft 21, the secondamplifier 37 that amplifies the output signal of the second sensor 34and outputs as the second sensor signal, the first voltage-dividingresistors Rd11 and Rd12 and the second voltage-dividing resistors Rd21and Rd22 that respectively divide the voltages of the first sensor powersource Vs1 and the second sensor power source Vs2 that are supplied bythe controller 40 via the harness 35, the first offset voltage outputcircuit 38 and the second offset voltage output circuit 39 that applythe offset voltage to the first amplifier 36 and the second amplifier 37to which the division voltages are respectively input from theconnection points of the first voltage-dividing resistors Rd11 and Rd12and the second voltage-dividing resistors Rd21 and Rd22, and thedecoupling capacitor C12 that connects the input terminal of the secondoffset voltage output circuit 39 and the ground.

The controller 40 includes the power management unit 50 that continuallysupplies the first sensor power source Vs1 and the second sensor powersource Vs2 when the power switch is on and stops supplying the firstsensor power source Vs1 when the power switch is off whileintermittently supplies power as the second sensor power source Vs2.

By arranging the decoupling capacitor C12, when the second sensor powersource Vs2 is intermittently supplied, even when the second sensor powersource Vs2 is switched, the voltage fluctuation in the power sourcecaused by the transient current is blocked by a low-pass filter formedby the voltage-dividing resistor Rd21 and the decoupling capacitor C12,and therefore the fluctuation in the DC component of the second sensorsignal is suppressed. As a result, the stability of the second sensorsignal can be improved.

(2) The sensor unit 30 may include bypass capacitors C23 and C24 thatconnect the power line of the second sensor power source Vs2 and theground at a position proximate to the second sensor 34.

By arranging bypass capacitors C23 and C24, the effect of theelectromagnetic noise occurred by the switching of the second sensorpower source Vs2 on the second sensor 34 is suppressed, and thereforethe stability of the second sensor signal can be improved.

(3) The controller 40 may include the decoupling capacitor C32 thatconnects the power line of the second sensor power source Vs2 of theharness 35 and the ground at a position proximate to the powermanagement unit 50.

By arranging the decoupling capacitor C32, the entry of the voltagefluctuation that occurs when the second sensor power source Vs2 isswitched into the harness 35 is prevented, and therefore the power canbe supplied by the harness 35 in a stable manner. Moreover, noisegenerated by the harness 35 can be reduced.

(4) The sensor unit 30 may include the bypass capacitors C21 and C22that connect the power line of the first sensor power source Vs1 and theground at a position proximate to the first sensor 33.

By arranging bypass capacitors C22 and C22, the effect of theelectromagnetic noise occurred by the switching of the first sensorpower source Vs1 on the first sensor 33 is suppressed, and therefore thestability of the first sensor signal can be improved.

The configurations of the first embodiment to the fourth embodiment maybe appropriately combined. For example, in the power control unit 56 ofthe power management unit 50 according to the third embodiment, thedrive interval of driving the second sensor 34 may be modified in theconfiguration and method similar to the power control unit 56 of thesecond embodiment.

Similar to the third embodiment, for example, the comparators 58 a and58 b according to the second embodiment may operate using the secondsensor power source Vs2 continually supplied from the third power supplyunit 54 as the power source and compare the threshold voltage Vr basedon the voltage of the second sensor power source Vs2 and the secondsensor signal when the ignition key 11 is on, and operate using thesecond sensor power source Vs2 as the power source intermittentlysupplied from the third power supply unit 54 and compare the thresholdvoltage Vr based on the voltage of the second sensor power source Vs2and the second sensor signal when the ignition key 11 is off, and thesine counter 58 c and the cosine counter 58 d may operate using theinternal power source Vp as the power source.

A bypass capacitor similar to that of the fourth embodiment may beprovided in the sensor units 30 and the controllers 40 according to thefirst to third embodiments, for example.

Variation

In the above description, the rotation angle detection device of thepresent invention is applied to an electric power steering device of acolumn-assist type, so-called upstream assistance type, however, therotation angle detection device of the present invention may be appliedto an electric power steering device of a so-called downstreamassistance type. Hereinafter, as an example of an electric powersteering device of the downstream assist type, configuration examples ofapplying the rotation angle detection device of the present invention toelectric power steering devices of single pinion-assist type, rackassist type, and dual pinion-assist type are described.

In the case of the downstream assist method, the motor 20, the sensorunit 30, and the controller 40 may not be separated but may be anintegrated structure Motor Control Unit (MCU) as illustrated by thebroken lines in FIG. 23 to FIG. 25 for waterproof purposes. In thiscase, a sensor IC that becomes the above-described first sensor 33 andsecond sensor 34 may be embedded in the circuit substrate of thecontroller 40.

FIG. 23 illustrates a configuration example of applying the rotationangle detection device of the present invention to a singlepinion-assist type electric power steering device. A column shaft 2 isprovided instead of column shafts 2 i and 2 o and a torsion bar thatconnects both. A steering wheel 1 is connected to a universal joint 4Aat one end of an intermediate shaft via a column shaft 2. The otheruniversal joint 4B is connected to an input-side shaft 4C of the torsionbar (not illustrated).

A pinion and rack mechanism 5 includes a pinion shaft 5A, a pinion gear5B, and a rack bar 5C. The input-side shaft 4C and the pinion rackmechanism. 5 are connected by a torsion bar (not illustrated) thattwists according to a difference of rotation angles of the input-sideshaft 4C and the pinion rack mechanism 5. A torque sensor 10electromagnetically measures a torsion angle of the torsion bar assteering torque Th of the steering wheel 1.

The pinion shaft 5A is connected to a motor 20 that assists the steeringforce of a steering wheel 1 via a reduction gear 3, and a sensor unit 30calculates rotation angle information of the motor rotation shaft of themotor 20, in a similar manner to the above-described embodiment.

FIG. 24 illustrates a configuration example of applying the rotationangle detection device of the present invention to a rack assist typeelectric power steering device. A spiral groove (not illustrated) isformed on a circumference surface of the rack bar 5C, and a spiralgroove (not illustrated) having a similar lead is formed inside a nut7A. A ball screw is formed by arranging multiple rolling bodies on arolling path formed by the spiral grooves.

A belt 7D is wrapped around a driven pulley 7C connected to the nut 7Aand the driving pulley 7B connected to the rotation shaft 20 a of themotor 20 that assists the steering force of the steering wheel 1, and arotary motion of the rotation shaft 20 a is converted to a linear motionof the rack bar 5C. A sensor unit 30 calculates rotation angleinformation of the motor rotation shaft of the motor 20, similar to theabove-described embodiment.

FIG. 25 illustrates a configuration example of applying the rotationangle detection device of the present invention to a dual pinion-assisttype electric power steering device. A dual pinion-assist type electricpower steering device includes a second pinion shaft 8A, a second piniongear 8B in addition to a pinion shaft 5A and a pinion gear 5B, and therack bar 5C includes a first rack tooth (not illustrated) that mesheswith the pinion gear 5B and a second rack tooth (not illustrated) thatmeshes with the second pinion gear 8B.

The second pinion shaft 8A is connected to a motor 20 that assists thesteering force of a steering wheel 1 via a reduction gear 3, and asensor unit 30 calculates rotation angle information of the motorrotation shaft of the motor 20, in a similar manner to theabove-described embodiment.

Reference Signs List

-   -   1 Steering wheel    -   2 i Column shaft (input shaft)    -   2 o Column shaft (output shaft)    -   3 Reduction gear    -   4A, 4B Universal joint    -   5 Pinion rack mechanism    -   6 Tie rod    -   10 Torque sensor    -   11 Ignition key (power switch)    -   12 Vehicle speed sensor    -   14 Battery    -   20 Motor    -   30 Sensor unit    -   33 First sensor    -   34 Second sensor    -   35 Harness    -   36 First amplifier    -   37 Second amplifier    -   38 First offset voltage output circuit    -   39 Second offset voltage output circuit    -   40 Controller    -   50 Power management unit    -   51 Regulator    -   52 First power supply unit    -   53 Second power supply unit    -   54 Third power supply unit    -   55 Internal power generation unit    -   56 Power control unit    -   57 Sensor power determination unit    -   58 Rotation number detection unit    -   58 a First comparator    -   58 b Second comparator    -   58 c Sine counter    -   58 d Cosine counter    -   60 Microprocessor    -   61 Angular position calculation unit    -   62 Count total unit    -   63 Rotation number information correction unit    -   63 a First quadrant information calculation unit    -   63 b Second quadrant information calculation unit    -   63 c Quadrant comparison unit    -   63 d Correction unit    -   64 Rotation number calculation unit    -   65 Angle calculation unit    -   66 Rotation angle information calculation unit    -   66 a, 66 c Multiplier    -   66 b, 66 d Adder    -   67 Diagnosis unit    -   68 Assist control unit    -   C11, C12, C31, C32 Decoupling capacitor    -   C21 to C24, Ce1, Ce2 Bypass capacitor

The invention claimed is:
 1. A rotation angle detection devicecomprising: a first sensor that is supplied with power when a powerswitch is on and outputs a first sensor signal in accordance with arotation of a motor rotation shaft of a motor, and to which power supplyis stopped when the power switch is off; an angular position calculationunit that is supplied with power when the power switch is on andcalculates angular position information representing an angular positionof the motor rotation shaft based on the first sensor signal, and towhich power supply is stopped when the power switch is off; a secondsensor that outputs a second sensor signal including a sine-wave signaland a cosine-wave signal in accordance with a rotation of the motorrotation shaft; a power management unit that supplies first power thatis continuous power to the second sensor when the power switch is on,supplies second power that is intermittent power having a voltage lowerthan a voltage of the first power to the second sensor when the powerswitch is off, and outputs rotation number information representing arotation number of the motor rotation shaft based on the second sensorsignal; and a rotation angle calculation unit that is supplied withpower when the power switch is on and calculates rotation angleinformation representing a rotation angle of the motor rotation shaftbased on the angular position information and the rotation numberinformation, and to which power supply is stopped when the power switchis off, wherein the power management unit includes: a power supply unitthat generates the first power and the second power; a comparator; and acounter that detects a rotation number of the motor rotation shaft bycounting an output of the comparator, wherein the comparator comparesthe second sensor signal and a reference voltage of a first voltagebased on the voltage of the first power when the power switch is on,when the power switch is turned off from on, the reference voltage to becompared to the second sensor signal by the comparator is switched fromthe first voltage to a second voltage based on the voltage of the secondpower, and the second voltage is lower than the first voltage.
 2. Therotation angle detection device according to claim 1, wherein the powersupply unit supplies the first power to the counter when the powerswitch is on, generates third power that is continuous power having asame voltage as the second power and supplies to the counter when thepower switch is off.
 3. The rotation angle detection device according toclaim 2, wherein: the power management unit includes a regulator thatgenerates fourth power that is continuous power having a first regulatorvoltage from an external power source when the power switch is on andgenerates fifth power that is continuous power having a second regulatorvoltage lower than the first regulator voltage from the external powersource when the power switch is off.
 4. The rotation angle detectiondevice according to claim 1, wherein the comparator and the power supplyunit are arranged in a single integrated circuit chip.
 5. The rotationangle detection device according to claim 1, wherein a time width of oneintermittent output of the second power is less than or equal to 220μsec. when the power switch is off.
 6. The rotation angle detectiondevice according to claim 5, wherein a time width of one intermittentoutput of the second power is set in accordance with a time constant ofthe second sensor signal when the second power is intermittentlysupplied.
 7. An electric power steering device comprising: a torquesensor configured to detect steering torque that is applied to asteering shaft based on a torsion angle between an input shaft and anoutput shaft connected via a torsion bar mounted on a steering shaft ofa vehicle; a motor configured to provide steering assistance force to asteering mechanism of the vehicle; a rotation angle detection devicecomprising: a first sensor that is supplied with power when a powerswitch is on and outputs a first sensor signal in accordance with arotation of a motor rotation shaft of the motor, and to which powersupply is stopped when the power switch is off; an angular positioncalculation unit that is supplied with power when the power switch is onand calculates angular position information representing an angularposition of the motor rotation shaft based on the first sensor signal,and to which power supply is stopped when the power switch is off; asecond sensor that outputs a second sensor signal including a sine-wavesignal and a cosine-wave signal in accordance with a rotation of themotor rotation shaft; a power management unit that supplies first powerthat is continuous power to the second sensor when the power switch ison, supplies second power that is intermittent power having a voltagelower than a voltage of the first power to the second sensor when thepower switch is off, and outputs rotation number informationrepresenting a rotation number of the motor rotation shaft based on thesecond sensor signal; and a rotation angle calculation unit that issupplied with power when the power switch is on and calculates rotationangle information representing a rotation angle of the motor rotationshaft based on the angular position information and the rotation numberinformation, and to which power supply is stopped when the power switchis off, wherein the power management unit of the rotation angledetection device includes: a power supply unit that generates the firstpower and the second power; a comparator; and a counter that detects arotation number of the motor rotation shaft by counting an output of thecomparator, wherein, the comparator compares the second sensor signaland a reference voltage of a first voltage based on the voltage of thefirst power when the power switch is on, when the power switch is turnedoff from on, the reference voltage to be compared to the second sensorsignal by the comparator is switched from the first voltage to a secondvoltage based on the voltage of the second power, and with respect torotation angle detection device, the second voltage is lower than thefirst voltage, wherein the rotation angle detection device is configuredto calculate rotation angle information of the motor rotation shaft ofthe motor; a motor control unit configured to drive and control themotor based on the steering torque; and a steering angle calculationunit configured to calculate a steering angle of the input shaft basedon the torsion angle, a reduction ratio of a reduction gear, and therotation angle information.
 8. A control method of an electric powersteering device, the electric power steering device comprising: a torquesensor configured to detect steering torque that is applied to asteering shaft based on a torsion angle between an input shaft and anoutput shaft connected via a torsion bar mounted on a steering shaft ofa vehicle; a motor configured to provide steering assistance force to asteering mechanism of the vehicle; and a rotation angle detection devicecomprising: a first sensor that is supplied with power when a powerswitch is on and outputs a first sensor signal in accordance with arotation of a motor rotation shaft of a motor, and to which power supplyis stopped when the power switch is off; an angular position calculationunit that is supplied with power when the power switch is on andcalculates angular position information representing an angular positionof the motor rotation shaft based on the first sensor signal, and towhich power supply is stopped when the power switch is off; a secondsensor that outputs a second sensor signal including a sine-wave signaland a cosine-wave signal in accordance with a rotation of the motorrotation shaft; a power management unit that supplies first power thatis continuous power to the second sensor when the power switch is on,supplies second power that is intermittent power having a voltage lowerthan a voltage of the first power to the second sensor when the powerswitch is off, and outputs rotation number information representing arotation number of the motor rotation shaft based on the second sensorsignal; and a rotation angle calculation unit that is supplied withpower when the power switch is on and calculates rotation angleinformation representing a rotation angle of the motor rotation shaftbased on the angular position information and the rotation numberinformation, and to which power supply is stopped when the power switchis off, wherein the power management unit includes: a power supply unitthat generates the first power and the second power; a comparator; and acounter that detects a rotation number of the motor rotation shaft bycounting an output of the comparator, wherein the comparator comparesthe second sensor signal and a reference voltage of a first voltagebased on the voltage of the first power when the power switch is on,when the power switch is turned off from on, the reference voltage to becompared to the second sensor signal by the comparator is switched fromthe first voltage to a second voltage based on the voltage of the secondpower, and the second voltage is lower than the first voltage; andwherein the rotation angle detection device is configured to calculaterotation angle information of a motor rotation shaft of the motor; theelectric power steering device further comprising: a motor control unitconfigured to drive and control the motor based on the steering torque;and a steering angle calculation unit configured to calculate a steeringangle of the input shaft based on the torsion angle, a reduction ratioof a reduction gear, and the rotation angle information, the controlmethod comprising: controlling the steering assistance force applied bythe motor based on the steering angle calculated by the steering anglecalculation unit.
 9. The electric power steering device according toclaim 7, further comprising a vehicle speed sensor configured to detecta speed of the vehicle, wherein the motor control unit is furtherconfigured to drive and control the motor based on the vehicle speed.